Characterization of Crystalline Structure and Morphology of Ga<sub>2</sub>O<sub>3</sub> Thin Film Grown by MOCVD Technique
Growth of gallium oxide thin film was realized with MOCVD on (0001) sapphire substrate. Structural and compositional properties of thin film were studied employing trimethylgallium and water as precursors, carrier gases were H2 and N2. Obtained film is polycrystalline and predominantly consisted of (201) oriented β-Ga2O3. Sample exhibited blue luminescence which is attributed to oxygen vacancies. H2 gas proved to have beneficial effect on film quality and overall growth process.
Absorption and luminescence in amorphous SixGe1-xO2 films fabricated by SPCVD
Abstract Optical absorption and photoluminescence of Ge-doped silica films fabricated by the surface-plasma chemical vapor deposition (SPCVD) are studied in the 2–8 eV spectral band. The deposited on silica substrate films of about 10 μm in thickness are composed as x·GeO2-(1-x)·SiO2 with x ranging from 0.02 to 1. It is found that all as‐deposited films do not luminesce under the excitation by a KrF (5 eV) excimer laser, thus indicating lack of oxygen deficient centers (ODCs) in them. After subsequent fusion of silicon containing (x
Radiation processes in oxygen-deficient silica glasses: Is ODC(I) a precursor of E′-center?
Abstract The accumulation of radiation-induced defects under non-destructive X-ray and destructive cathodoexcitation was studied in pure silica KS-4V glasses possessing an absorption band at 7.6 eV. The correspondence between the existence of this band and the creation of the E′-center by radiation was checked. Detection of induced defects was accomplished by measurement of the luminescence during irradiation, post irradiation afterglow or phosphorescence, induced optical absorption, and thermally stimulated luminescence. In all samples, these observed phenomena associated with charge trapping and recombination on the oxygen-deficient luminescence center. Others centers of luminescence were…
Localized states in wide-gap oxide glasses
Localized states manifest themselves by light absorption at the optical gap of a glass and by luminescence excited there with Stoke's shift. They are created by the minority structural motifs of one or many structural modifications in which a material can exist, and which can provide electronic states absorption at the optical gap. Their wavefunctions overlapping determine the luminescence intensity dependence on the temperature [I(T)on the order of magnitude exp(- T/T 0 )] and power law (t -1 ) of luminescence decay kinetics, which include intra-center processes due to triplet-singlet transitions and recombination processes due to a tunnel and overbarrier transitions, as well as a fast com…
Luminescence of fluorine-doped and non-doped silica glass excited with an ArF laser
Abstract The role of fluorine doping on silica has been studied through comparison of the luminescence of fluorine doped and fluorine-free samples made by melting in on SiF4 atmosphere and excited by an ArF laser (6.4 eV) in the temperature range 10–290 K. The fluorine doped sample possesses a very weak absorption band at 7.6 eV on the level of 0.1 cm−1 and there the photoluminescence of so-called oxygen-deficient centers in the blue (2.7 eV) and UV bands (4.4 eV) could be excited. The same luminescence bands are observable in the fluorine-free sample, which contains an absorption band at 7.6 eV on the level of 20 cm−1. In the fluorine-doped sample the UV band prevails over the blue band. T…
Impact of fluorine admixture, hydrogen loading, and exposure to ArF excimer laser on photoluminescence of bismuth defects in amorphous silica
Abstract Photoluminescence (PL) excited by ArF (193 nm), KrF (248 nm) and N 2 (337 nm) pulsed lasers is studied in bismuth doped unfused silicon dioxide synthesized on silica substrates by surface-plasma chemical vapor deposition (SPCVD). Additive free and fluorinated (F content ~ 0.4 wt.%) amorphous silica are examined as host materials for bismuth. Three typical PL bands peaking at wavelengths of 650 nm (orange), 800 nm and 1400 nm (near infrared, NIR) were observed. It is found that fluorine additive weakly affects PL detail of as deposited samples. However, hydrogen loading completely deactivates NIR PL in the case of fluorine free sample, but only slightly suppresses the NIR band in fl…
E-beam induced damage in SiO2–Ge crystalline α-quartz, comparison with silica glass
Electron beam induced transformation in crystalline α-quartz doped with germanium was studied by mean of cathodoluminescence and of phase shift interferometric microscope. E-beams with low current (below 50 nA), defocused (diameter of spot about 40 μm) and with acceleration energy of 15 kV produce swelling of the irradiated volume about 100 nm above the non-irradiated surface. The luminescence of the self-trapped near germanium exciton (GeSTE) is observed mainly. No luminescence of the germanium related oxygen deficient center with bands at 290 and at 395 nm, usual for Ge-doped silica glass (GeODC), was observed. Defocused e-beam with higher current (about 200 nA), the same energy and simil…
Luminescence of localized states in oxidized and fluorinated silica glass
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.
Electron beam induced optical and electronical properties of SiO 2
Abstract Ionizing radiation in dielectric and optically transparent silica as well as thin SiO 2 layers produces defect luminescence as well as charge storage. A comparison of different excitation–relaxation processes like cathodoluminescence, charge injection and trapping, secondary electron field emission, and exoelectron emission leads to a generally similar excitation dose behaviour described by an electron beam saturation dose of 0.01–0.1 C/cm 2 . This suggests a correlation of these four electron excitation mechanisms likely related to the same kind of defect in glassy SiO 2 , the 2-fold-coordinated silicon Si: centre with typical electronic singlet–singlet and singlet–triplet transit…
Silicon dioxide thin film luminescence in comparison with bulk silica
Abstract The luminescence of the self-trapped exciton (STE) in SiO2 films was measured at low temperatures on the background of defect luminescence under cathodoexcitation and compared with bulk silica luminescence. The defect luminescence is mainly caused by non-bridging oxygen centers (a red luminescence band at 1.8 eV) and twofold coordinated silicon centers (blue and ultraviolet luminescence with 2.7 and 4.4 eV bands, respectively). The STE luminescence with a band at 2.3 eV is uniformly distributed within SiO2 film volume. Contrary to defect luminescence, whose intensity increases with irradiation time, the STE luminescence decreases almost to zero in a few seconds of irradiation time.…
Self-trapped exciton in Li2GeO3
Abstract Self-trapped excitons (STE) are discovered in Li2GeO3 crystal. The PL band at 2.7 eV with a strong Stoke's shift is excited in the intrinsic absorption range of Li2GeO3 crystal, in which the optical gap is situated at 6 eV. The activation energy of the STE luminescence thermal quenching is not monoenergetic and is situated in the range 40–100 meV. The luminescence is strongly polarized. The decay kinetics can be characterized by τ = 0.9 ms at 45 K. At 5 K it can be approximated by fast (0.6 ms) and slow (4–2.5 ms) components. Decay kinetics is determined by triplet state of STE splits in zero magnetic field. Two different excited triplet states (centers) have the average ODMR param…
Thermostimulated luminescence and electron spin resonance in X-ray- and photon-irradiated oxygen-deficient silica
Abstract Influences of oxygen-deficiency on radiation properties of high-purity, low-OH fused silica were studied. It is found that thermostimulated luminescence (TSL) peaks are different for photo (7.7 eV) and X-ray excitation at 77 K. X-ray excitation produces TSL peaks at 125 and 170 K corresponding to the anneal temperatures of two types of self-trapped holes centers STH2 and STH1, respectively, detected by electron spin resonance (ESR). Oxygen-deficiency apparently increases the number of electron traps, stabilizing a larger number of STHs in the continuous defect-free silica network than is observed in similarly X-irradiated stoichiometric silica glasses. Photoexcitation of oxygen-def…
Photoluminescence excited by ArF and KrF lasers and optical absorption of stishovite mono-crystal
Two photoluminescence bands were found in a stishovite (silicon dioxide) mono-crystal sample under ArF (193 nm) and KrF (248 nm) excitation. The blue band is situated at 3.17 ± 0.02 eV in the case of ArF and at 3 ± 0.2 in the case of KrF. The UV band is at 4.55 ± 0.05 eV in the case of ArF and at 4.5 ± 0.05 eV in the case of KrF. The position of the UV emission band correlates with that excited by x rays. This position is 4.6 ± 0.05 eV with FWHM 0.8 ± 0.05 eV (Truhins et al 2003 Solid State Commun. 127 415). The blue band possesses slow decay kinetics with time constant 16 ± 2 µs and the UV band is fast on the level of 2 ± 0.5 ns, similarly for both lasers. Thermal quenching of both bands b…
Energy transport in silica to oxygen-deficient luminescence centers. Comparison with other luminescence centers in silica and α-quartz
Abstract The transport of energy absorbed by silica glass to oxygen-deficient luminescence centers in was studied in the range of intrinsic absorption from 8.2 up to 35 eV. The low efficiency of exciting those luminescence centers by transport of energy could not be ascribed merely to carrier scattering by the disordered structure. Other centers (Cu + , for example) could be excited in such process with sufficiently high efficiency, albeit lower than that in crystals. The low efficiency of interaction of oxygen deficient centers with quasi-particles is attributed to isolation of these centers in clusters and the non-radiative annihilation of the quasi-particles on the boundaries of these cl…
Radiation induced defects in SiO 2
The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) …
Photoluminescence in gamma-irradiated alpha-quartz investigated by synchrotron radiation
Abstract We report an experimental investigation of the photoluminescence, under excitation by synchrotron radiation within the absorption band at 7.6 eV , induced in γ-irradiated α-quartz. Two emissions centered at 4.9 and 2.7 eV are observed at low temperature: the former decreases above 40 K , whereas the second band exhibits an initial slight increase and its quenching is effective above 100 K . Furthermore, the decay kinetics of both emissions occur in a time scale of nanoseconds: at T=17.5 K we measured a lifetime τ∼1.0 ns for the photoluminescence at 4.9 eV and τ∼3.6 ns for that at 2.7 eV . These results give new insight on the optical properties associated with defects peculiar of c…
Raman and optical reflection spectra of germanate and silicate glasses
Abstract Germanate and phosphosilicate glasses made in oxygen surplus conditions were studied by Raman and optical reflection methods. We found that the optical reflection spectra of the germanate glasses are quite similar to the one those of a GeO 2 crystal with the α-quartz structure. The reflection of phosphosilicate glasses is very close to silica glass-related spectra. Hence, the determining influence of the tetrahedral structure on reflection spectra is revealed. The Raman spectra of germanate samples are similar to those reported the one known in the literature. Octahedral entities, namely bands similar to stishovite vibration modes, were difficult to detect in phosphosilicate glasse…
Self-trapped exciton luminescence in crystalline α-quartz under two-photon laser excitation
Abstract The luminescence of pure crystalline α-quartz is studied under pulsed ArF laser excitation. The luminescence parameters obtained correspond well with those of self-trapped excitons (STEs) in α-quartz, indicating that the excitation process is two-photon. The efficiency of two-photon excitation is of the same order of magnitude as the one-photon excitation of sodium salicylate. The STE luminescence decay kinetics and their temperature dependence under photoexcitation were recorded with higher accuracy than previously. Changes in the decay kinetics with temperature are explained by the splitting of the STE triplet state in zero magnetic field and are analyzed with the assumption of t…
Intrinsic absorption threshold of stishovite and coesite
Abstract The optical absorption spectra of the small mono-crystals samples of stishovite and coesite were studied at first. The intrinsic absorption threshold of stishovite is determined at 8.75 eV, being probably, highest in the family of different crystalline polymorph modifications of silicon dioxide. The absorption spectrum of stishovite is independent of temperature (studied in the range 290–450 K). The intrinsic absorption threshold of coesite mono-crystal situated near 8.6 eV at 293 K, coincides within experimental errors with that of α-quartz crystal, and depends on temperature, as used to be for the tetrahedron structured silicon dioxide crystalline modifications. A broad absorptio…
Luminescence of rutile structured crystalline silicon dioxide (stishovite)
Abstract Luminescence spectrum of synthetic mono-crystalline stishovite comprises a slow blue band at ~400 nm (~3.1 eV) and a fast UV band at ~260 nm (~4.7 eV), as well as some bands in near-infrared range of spectra. The NIR luminescence of stishovite crystal, excited with lasers 532 nm, 248 nm and 193 nm as well as x-ray, possesses several sharp lines. A zero phonon line is situated at 787 nm (1.57 eV) and grows with cooling. An anti-Stokes line is located at 771 nm (1.68 eV). This line disappears with cooling. In a powder sample of stishovite created by shock waves generated by the impact of a 50-m-diameter meteorite in Arizona 50,000 years ago, the PL broad blue band is situated at 425 …
Ultraviolet luminescence of ScPO4, AlPO4 and GaPO4 crystals.
The luminescence of self-trapped excitons (STEs) was previously observed and described for the case of tetragonal-symmetry ScPO4 single crystals. The subject band in this material is situated in the UV spectral range of ?210?nm or ?5.8?eV. In the present work, we are both expanding this earlier luminescence study and seeking to identify similar luminescence phenomena in other orthophosphate crystals, i.e., AlPO4 and GaPO4. These efforts have proven to be successful?in spite of the structural differences between these materials and ScPO4. Specifically we have found that for AlPO4 and GaPO4, in addition to an ?-quartz-like STE, there is a UV luminescence band that is similar in position and d…
γ-ray induced GeODC(II) centers in germanium doped α-quartz crystal
International audience; Main luminescence of α-quartz crystal doped with germanium results from the luminescence of a self-trapped exciton (STE) near germanium. In as grown Ge-doped α-quartz crystal, the luminescence associated with the twofold coordinated Ge center (GeODC) in amorphous silica glass doped with germanium, was never observed. In this work, we performed experiments to investigate if a GeODC like luminescence could appear after a γ-irradiation of a Ge-doped α-quartz crystal. The answer is positive: under excitation with pulsed light of an ArF laser (193 nm): a new luminescence with two bands -- a blue one associated to a time constant of about 100 μs appears and another one wit…
Photosensitivity of SiO2–Al and SiO2–Na glasses under ArF (193 nm) laser
Abstract Photosensitivity of SiO 2 –Al and SiO 2 –Na glass samples was probed by means of the induced optical absorption and luminescence as well as by electron spin-resonance (ESR) after irradiation with excimer-laser photons (ArF, 193 nm). Permanent visible darkening in the case of SiO 2 –Al and transient, life time about one hour, visible darkening in the case of SiO 2 –Na was found under irradiation at 290 K. No darkening was observed at 80 K for either kind of material. This investigation is dedicated to revealing the electronic processes responsible for photosensitivity at 290 and 80 K. The photosensitivity of both materials is related to impurity defects excited directly in the case …
Excitation processes of the blue luminescence in crystalline SiO 2 probed by synchrotron radiation measurements
Luminescence properties of crystalline α-quartz were investigated by time-resolved spectroscopy under pulsed synchrotron radiation excitation in the vacuum ultraviolet range. Our results evidence that two emission bands overlap at 2.7 eV, both being observed only at low temperature. The first contribution is excited by band-to-band transition and is related to the radiative recombination of a self trapped exciton occurring in a time scale of a few ms, the second is associated with defects induced in quartz by γ- and β-radiation, is excited at 7.6 eV and its lifetime is 3.6 ns at T = 10 K. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence of dense, octahedral structured crystalline silicon dioxide (stishovite)
Abstract It is obtained that, as grown, non-irradiated stishovite single crystals possess a luminescence center. Three excimer pulsed lasers (KrF, 248 nm; ArF, 193 nm; F 2 , 157 nm) were used for photoluminescence (PL) excitation. Two PL bands were observed. One, in UV range with the maximum at 4.7±0.1 eV with FWHM equal to 0.95±0.1 eV, mainly is seen under ArF laser. Another, in blue range with the maximum at 3±0.2 eV with FWHM equal to 0.8±0.2 eV, is seen under all three lasers. The UV band main fast component of decay is with time constant τ =1.2±0.1 ns for the range of temperatures 16–150 K. The blue band decay possesses fast and slow components. The fast component of the blue band deca…
Luminescence of coesite
Coesite is a polymorph modification of crystalline silicon dioxide with a tetrahedral structure. The luminescence of a single crystal of synthetic coesite was studied under excitation using x-rays, an electron beam, and excimer lasers KrF (248 nm), ArF (193 nm) and F2 (157 nm). Luminescence bands in the regions of 2.5 eV and 4.4 eV appear. The blue band is dependent on temperature and is composed of decay kinetics. Three main decay times are revealed, exhibiting luminescence of a different nature in the same range of the spectrum. One is in the ns range of time with a time constant of about 2 ns. The two other decay times are in the regions of 5 μs and 700 μs. The 5 μs component is also see…
Photosensitivity of silica glass with germanium studied by photoinduced of thermally stimulated luminescence with vacuum ultraviolet radiation
Photosensitivity of the germanium-doped silica was studied through kinetics of recombination of the created defects in isothermal and thermally stimulated luminescence (TSL) regimes. The main observed luminescence contains bands mainly due to Ge oxygen deficient center. The maximum of photosensitivity corresponds to the high-energy part of the 7.6 eV band. The growth of TSL intensity is almost linear for the case of excitation through monochromatic light and growth with saturation in the case of excitation with white light. The efficiency of formation of TSL peaks increases with an increase of the temperature. The result was explained as multi-step process of photochemical dissociation and …
host‐defect luminescence of stishovite
a detailed study of the 4.75 eV luminescence band of stishovite single crystal (SiO2 with rutile structure) is reported. Kinetics of luminescence intensity is studied at durable (tens of minutes) X-ray excitation. The observed behaviour of the band intensity is explained by creation and destruction of luminescence centres depending on temperature both being determined by radiation stimulated diffusion of atomic particles. The luminescence decay is observed to last for minutes after X-ray irradiation while only for ns and hundreds of µs under pulsed e-beam irradiation suggesting a complicated recombination of the created defects. The UV band of stishovite is compared with the 4.9 eV luminesc…
Photoelectric response of localized states in silica glass
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.
Study of the germanium luminescence in silica: from non-controlled impurity to germano-silicate core of telecommunication fiber preforms
Abstract We have studed luminescence properties of doped silica with different concentrations of germanium. The basic luminescence parameters such as spectral dependencies, decay kinetics and polarization at different temperatures were measured. Three spectral ranges 3.5–5.5 eV(I), 5.5–7 eV(II), 7–8 eV(III) in the optical transparency range of silica could be chosen from these data. Range I possesses a weak variation of basic parameters of luminescence of the germanium related oxygen deficient center with the change of luminescence center concentration from extremely low in pure silica to the germano-silica core of optical telecommunication fiber preforms. The temperature dependence of lumi…
Dynamics of Singlet Oxygen Molecule Trapped in Silica Glass Studied by Luminescence Polarization Anisotropy and Density Functional Theory
The support from M-ERANET project “MyND” is acknowledged. A.A., M.M-S., and L.R. were supported by the Research Council of Lithuania (Grant M-ERA.NET-1/2015). The authors thank A. Pasquarello for providing the structures of the amorphous SiO 2 matrix for our computational work and K. Kajihara (Tokyo Metropolitan University) for valuable advice in PL kinetics measurements.
The correlation of the 7.6 eV optical absorption band in pure fused silicon dioxide with twofold-coordinated silicon
Abstract The optical absorption band at 7.6 eV, which appears in oxygen deficient pure silica, does not correlate with any ESR signal in non-irradiated samples. Longlasting illumination at 80 K in the range of its absorption leads to an increase of the absorption band at 5 eV. Subsequent heating to 290 K restores the initial absorption. These data can be explained as photodissociation and thermal recreation of a complex defect containing a twofold-coordinated silicon defect. This complex defect is responsible for the 7.6 eV absorption band.
Luminescence of fluorine doped silica glass
Abstract The role of fluorine doping on silica properties was studied by luminescence methods. Non-doped samples of the same preparation technology possess an absorption band at 7.6 eV on the level of 2 cm−1. A trace of this band in the fluorine-doped sample is on the level of 0.1 cm−1. In both samples 7.6 eV photons as well as ionizing irradiation (X-ray, electron beam) excite photoluminescence of so-called oxygen deficient centers with a blue (2.7 eV) and a UV band (4.4 eV). The luminescence of the fluorine doped sample increases with dose many times from the initial low level for the same excitation. Also, thermally stimulated luminescence appears after irradiation. The energetic yield u…
Absorption and luminescence in amorphous silica synthesized by low-pressure plasmachemical technology
A comparison study of as-deposited by the hydrogen-free SPCVD process silicon dioxide with and without fluorine as well as the one in the form of fused materials is performed to define whether glass forming processing affects its optical properties. Raman scattering, optical absorption in the vacuum ultraviolet region as well as luminescence at different temperatures and various excitation conditions are measured. A difference in Urbach rule parameters and intrinsic defect concentrations for different samples is revealed. No significant impact on the structure responsible for Raman scattering is observed.
Investigation of optical and radiation properties of oxygen deficient silica glasses
The deficiency of oxygen in pure silica manifests an absorption band at 5 eV as well as an absorption band of higher intensity at 7.6 eV. The band at 5 eV is associated with lone twofold-coordinated silicon centers. The nature of the main band at 7.6 eV has been studied using silica samples with different levels of oxygen deficiency. The excitation via the 7.6 eV band produces a photoelectric response as well as inner center and recombination type luminescence. Two main luminescence bands of the twofold-coordinated silicon center appear: a blue band (2.7 eV) and a UV band (4.4 eV). Induced absorption with several bands as well as thermally stimulated luminescence with complex peak structure…
Luminescence of localized states in silicon dioxide glass. A short review
Abstract The target is the description of the properties of localized states in silica glass, which relate to aspects of short-to-intermediate-range order. It has been observed that laser light interaction with localized states of silica glass leads to the creation of luminescence centers. Created luminescence centers, excited with laser light, provide intra-center luminescence of oxygen deficient centers (ODC) comprising a blue band at 2.7 eV and a UV band at 4.4 eV. Structurally, these ODCs are understood to comprise twofold-coordinated silicons that are commonly part of some larger local structure, and their luminescence bands can be suppressed by reaction with chlorine or hydrogen. Besi…
Luminescence of γ-radiation-induced defects in α-quartz
Optical transitions associated with γ-radiation-induced defects in crystalline α-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy γ-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it…
Luminescence of a self-trapped exciton in GeO2 crystal
Abstract The self-trapped exciton (STE) is discovered in the GeO2 crystal. A PL band at 2.5 eV with a strong Stokes shift is excited only in the fundamental absorption range of GeO2 crystal with the quantum yield about 0.4 and the decay time constant 800 ± 5 μs at 80 K. The PL thermal quenching occurs at 200 K with the energy about 0.25 eV and the frequency factor 107. At 4.5 K the PL decay kinetics splits into two components with time constants 270 μs and 8000 μs, which can be due to a triplet state split in the zero magnetic field. The STE in GeO2 is very similar to a STE in SiO2.
Luminescence of polymorph crystalline and glassy SiO2, GeO2: A short review
Studies of SiO 2 and GeO 2 crystals with α-quartz and rutile structures were performed during last two decades. The goal of such studies was comparison of properties with those of glassy modifications of these crystals. Luminescence of oxygen deficient centers in these glassy materials was found to resemble the luminescence of the rutile-type modification rather than α-quartz modification. In α-quartz, similar luminescence centers appear after damaging irradiation by electron beam at low temperatures (<60 K) or at ambient temperatures after gamma or neutron irradiation.
Excitons in SiO2: a review
Abstract In this paper, excitonic properties of crystalline and glassy SiO 2 are reviewed. Experimental spectroscopic data (optical absorption and reflection spectra, as well as spectra of luminescence and its excitation), luminescence decay kinetics at different temperatures, and photoelectric properties — photoconductivity and photoelectron emission — were used to determine excitons in SiO 2 . Information on migration of excitons was obtained on the basis of energy transport to impurity luminescence centers, the latter being detectors of quasiparticles. Determination of excitonic properties in glassy SiO 2 was based on the comparison of the observed phenomena in crystalline and glassy mat…
<title>Localized excitons in fluoroperovskite LiBaF<formula><inf><roman>3</roman></inf></formula> crystals</title>
Two radiating processes in LiBaF3 crystals, fast valence-core transitions (5.4 - 6.5 eV) and slow, so called self-trapped exciton luminescence (about 4.3 eV), are important for practical application. Here we present a study of 4.3 eV luminescence under X-ray excitation and photoexcitation as well as under photostimulation after X-irradiation of undoped and Ag-doped LiBaF3 crystals at various temperatures. It is shown that 4.3 eV luminescence appears under X-ray excitation at least from 85 K to 400 K in both undoped and doped crystals. In all samples studied the excitation spectra of 4.3 eV luminescence contain both the main exciton like band at the edge of fundamental absorption at about 10…
Luminescence of different modifications of crystalline silicon dioxide: Stishovite and coesite
Abstract Luminescence of very small samples of single crystals of coesite and stishovite has been studied. The spectra were detected under ionizing radiation (X-ray and electron beam) and the decay kinetics of cathodoluminescence in the range of time from 10 ns to 3 ms was measured. The coesite luminescence possesses a broad band at 3 eV with exponential decay about 680 μs at 80 K. The nature of this luminescence was explained as a self-trapped exciton creation in tetrahedron framework. The stishovite luminescence possesses two bands—blue (2.8 eV) and UV (4.7 eV). The UV band intensity grows more than 20 times with irradiation dose from initial level. This shows that the corresponding lumin…
Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals
Abstract The luminescence of GeO 2 rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N 2 laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses…
Sub-band-gap-excited luminescence of localized states in SiO2–Si and SiO2–Al glasses
Abstract Silica glass samples doped with extra silicon (SiO 2 –Si: artificial oxygen deficiency) and with aluminum (SiO 2 –Al: Al-doped without accompanying alkali ions) were studied. The luminescence properties of these two samples are compared in the range of temperature 15–290 K under excitation of ArF excimer laser (193 nm). In both samples the luminescence of oxygen deficient centers (ODCs) is detected, i.e., emission bands in the blue at 440 nm and the UV at 280 nm. Cooling of the both samples led to strong increases of luminescence intensity down to 80 K with much smaller increases for still lower temperatures. At 290 K in SiO 2 –Si a luminescence similar to that of twofold-coordinat…
Luminescence of natural α-quartz crystal with aluminum, alkali and noble ions impurities
This work was supported by the Latvian Science Council Grant No lzp-2018/1–0289 .
Luminescence of phosphorus containing oxide materials: Crystalline SiO2‐P and 3P2O5⋅7SiO2; CaO⋅P2O5; SrO⋅P2O5 glasses
Luminescence of phosphate glasses such as CaO⋅P2O5 and SrO⋅P2O5 is compared with that of phosphorus doped crystalline α-quartz and phosphosilicate glass with content 3P2O5⋅7SiO2. Water & OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5 - 5.5 eV. The luminescence bands in UV range at 4.5-5 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also a component in μs range was detected. PL band of μs component is shifted to low energy with respect to that of ∼37 ns component. This shift is about 0.6 eV. It is explained as singlet-triplet splitting of excited st…
Self-trapped exciton luminescence in α-quartz
Abstract It is shown that two differently oriented (perpendicular and parallel to the c axis) serf-trapped excitons (STE ⊥ and STE ∥ ) can be created in the range of the Urbach tail of the fundamental absorption of α-quartz. Below this tail no STE luminescence was found. The alkali ion centers, excited below the tail, give luminescence bands, which can be replaced by substituting alkali ions with Cu + ions. It is concluded that both STE ∥ and STE ⊥ are intrinsic.
Intra-center and recombination luminescence of bismuth defects in fused and unfused amorphous silica fabricated by SPCVD
Abstract Photoluminescence (PL) of bismuth doped silicon dioxide excited by UV excimer lasers (ArF — 193 nm, KrF — 248 nm) and a green light laser diode (532 nm) is studied in a wide spectral band at temperatures ranging from 12 to 750 K. Two types of samples are investigated: unfused, 100 μm in thickness amorphous layer immediately deposited on the inner surface of silica substrate tube, and the same material after profusion resulted from tube collapsing to a rod by external heating. PL bands centered at 620–650 nm, 820 nm and 1400 nm wavelengths are observed in both fused and unfused samples. Under excitation by the green laser diode decay time constants for 650 nm (orange) and 1400 nm (N…
Cathodoluminescence of crystalline and amorphous SiO2 and GeO2
Abstract Cathodoluminescence (CL) and its temperature-dose behaviour are presented for different crystalline and amorphous modifications of SiO 2 and GeO 2 as well as for Ge-doped SiO 2 layers. The crystalline samples include four-fold coordinated Si and Ge in hexagonal quartz and quartz-like crystals, respectively, as well six-fold coordinated atoms in tetragonal rutile-like crystals. The detected luminescence bands, in general, are attributed to three optical active luminescence centres: the two-fold coordinated silicon (=Si:) and germanium (=Ge:) centre, respectively, the non-bridging oxygen hole centre (NBOHC) and the self trapped exciton (STE). The first ones, the oxygen deficient cent…
Photoluminescence and Electron Spin Resonance of Silicon Dioxide Crystal with Rutile Structure (Stishovite)
This work was supported by ERANET MYND. Also, financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2017/2 realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. The authors express our gratitude to R.I. Mashkovtsev for help in ESR signal interpretation. The authors are appreciative to T.I. Dyuzheva, L.M. Lityagina, N.A. Bendeliani for stishovite single crystals and to K. Hubner and H.-J. Fitting for stishovite powder of Barringer Meteor Crater.
UV and yellow luminescence in phosphorus doped crystalline and glassy silicon dioxide
Abstract Luminescence of phosphorus doped crystalline α-quartz and phosphosilicate glass with content 3P2O5·7SiO2 was studied. Water and OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5–5.5 eV. The luminescence bands in UV range at 4.5–5 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also a component in µs range was detected. PL band of µs component is shifted to low energy with respect to that of ~37 ns component. This shift is about 0.6 eV. It is explained as singlet–triplet splitting of excited state. Below 14 K increase of luminescence kinetics du…
Recombination luminescence of oxygen-deficient centers in silica
Abstract The luminescence of silica glass, prepared by plasma chemical vapor deposition (PCVD) and quartz glass of type IV (trade mark KS-4V) methods, were studied while irradiated with pulses of ArF laser (193 nm) light in the range of sample temperatures between 10 and 300 K. The samples contain less than 0.1 ppm metallic and hydroxyl impurities. The samples synthesized by PCVD were of two kinds. The first one (amorphous) was as-deposited from plasma at a substrate tube temperature of ∼1200 °C. The second one (fused) was prepared from the first by the tube collapsing with an external burner. In this process, a section of the substrate tube with the deposited glass was installed in a lathe…
UV cathodoluminescence of crystalline α-quartz at low temperatures
Two luminescence bands in the UV range were detected in crystalline a-quartzunder electron beam excitation (6 kV, 3–5mA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (o10 ns) and a slow one in the range of 200ms. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline a-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation me…
Defect Luminescence Study in Tetragonal GeO2 Crystals
The perovskite-or rutile-like GeO2 crystals were grown by the “top-seed” method from a fused germanium dioxide solution with sodium bicarbonate. The luminescence was studied under cathode-, x-ray, and photo-excitation. There are two luminescence bands at 550 nm and 400 nm with slow (100–200 µs) and fast (<20 ns) decay, respectively. The luminescence can be excited either by intra-center and electron-hole recombination processes. An analogous luminescence, however with strong non-exponential decay, is observed in glassy materials obtained from the frozen solution. Sodium-germanate glasses melted under oxygen deficient condition also possess similar luminescence, therefore the luminescence is…
Luminescence of silica glass containing aluminum oxide
Abstract Optical properties of silica glass with different doping of Al 2 O 3 up to 1.5 mol% were studied. Alumina stimulates creation of a luminescence centers with specific band at 3.3 eV. A new band at 8.2 eV appears in luminescence excitation spectra. There is transport of energy to other luminescence centers associated with an impurity (Ag, Ce) at this energy. Alumina stimulates creation of E′ centers under γ-irradiation beside trapped hole on AlO 4 tetrahedron as well as creation of a silicon related oxygen deficient center (SiODC) under cathodoexcitation. Visually, the samples look inhomogeneous even after γ-irradiation. The explanation could be heterogeneity of the samples. Alumina …
Cathodoluminescence decay kinetics in Ge+, Si+, O+ implanted SiO2 layers
Abstract Cathodoluminescence spectral shapes and respective band decay times show no similarity between luminescence centers in different crystal and amorphous modifications of SiO2 and GeO2. On the other hand, the additionally produced red luminescence centers (650 nm) by oxygen implantation into SiO2 layers are of the same nature as in stoichiometric SiO2 and are attributed to the non-bridging oxygen hole center (NBOHC). On the other hand, the elevated blue luminescence (460 nm) in Si implanted SiO2 belongs to the silicon related oxygen deficient center (SiODC) as in stoichiometric layers also. Ge implantation into SiO2 and thermal post-annealing leads to a huge violet luminescence (400 n…
Peculiarities of photoluminescence excited by 157nm wavelength F2 excimer laser in fused and unfused silicon dioxide
Abstract Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F 2 excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperb…
Luminescence of unfused 95%SiO2–5%GeO2 amorphous films with fluorine additive: No evidence for presence of GeODC(I) defects found
Abstract Photoluminescence (PL) of unfused amorphous germanosilicate films with fluorine additive is studied in 2–8.5 eV spectral range. Experiments are based on films deposited on silica substrates by means of the surface-plasma chemical vapor deposition (SPCVD). Films of about 100 μm in thickness with “high F” (~ 4.2 wt.%) and “low F” (~ 0.5 wt.%) fluorine content have been fabricated for the experiments. KrF (248 nm), ArF (193 nm) and F2 (157 nm) excimer lasers are used to pump PL. It is found that absorption and luminescence associated with germanium oxygen deficient centers (GeODCs) in “high F” and “low F” films differ. In the “high F” unfused film absorption coefficient of the band at…
Cathodoluminescence of Ge+, Si+, and O+ implanted SiO2 layers and the role of mobile oxygen in defect transformations
Abstract Thermally grown SiO 2 layers of thickness d =500 nm have been implanted by Ge + , Si + , and O + ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of D i =5×10 16 ions/cm 2 . Thus the implantation profiles are expected with a concentration maximum of nearly 4 at.% at the half-depth d m ≅250 nm of the SiO 2 layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band ( λ =400 nm) of the Ge + implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. I…
Cathodoluminescence and IR absorption of oxygen deficient silica – influence of hydrogen treatment
Abstract The cathodoluminescence (CL) and IR absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, some samples have been treated in hydrogen at 800°C. Crystalline quartz was used for reference measurements and the CL data have been compared with those of X-ray excited luminescence (XL). The luminescence spectra of silica have a band at 1.85 eV due to non-bridging oxygens and the two bands at 2.7 and 4.4 eV due to twofold-coordinated silicons. The energetic yield for CL is about 0.1%, for XL it approaches 0.15%. Cathodoluminescence of quartz at temperatures >130 K exhibits the self-trapped exciton lumines…
Luminescence of polymorphous SiO2
Abstract The luminescence of self-trapped exciton (STE) was found and systematically studied in tetrahedron structured silica crystals (α-quartz, coesite, cristobalite) and glass. In octahedron structured stishovite only host material defect luminescence was observed. It strongly resembles luminescence of oxygen deficient silica glass and γ or neutron irradiated α-quartz. The energetic yield of STE luminescence for α-quartz and coesite is about 20% of absorbed energy and about 5(7)% for cristobalite. Two types of STE were found in α-quartz. Two overlapping bands of STEs are located at 2.5–2.7 eV. The model of STE is proposed as Si–O bond rupture, relaxation of created non-bridging oxygen (N…
Luminescence of silicon Dioxide — silica glass, α-quartz and stishovite
Abstract This paper compares the luminescence of different modifications of silicon dioxide — silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishov…
Luminescence of α-quartz crystal and silica glass under excitation of excimer lasers ArF (193 nm), KrF (248 nm)
This work is supported by Latvian National Program “IMIS2”. We are indebted to I.I. Cheremisin for crystal samples.
Luminescence of phosphorus doped silica glass
This work is supported by Material Science program IMIS2 of Latvia.