Search results for "SPECTRA"
showing 10 items of 3542 documents
Photoluminescence spectral dispersion as a probe of structural inhomogeneity in silica
2011
We perform time-resolved photoluminescence measurements on point defects in amorphous silicon dioxide (silica). In particular, we report data on the decay kinetics of the emission signals of extrinsic oxygen deficient centres of the second type from singlet and directly excited triplet states, and we use them as a probe of structural inhomogeneity. Luminescence activity in sapphire (alpha-Al(2)O(3)) is studied as well and used as a model system to compare the optical properties of defects in silica with those of defects embedded in a crystalline matrix. Only for defects in silica did we observe a variation of the decay lifetimes with emission energy and a time dependence of the first moment…
Nature of the blue luminescence bands in PbWO4
1997
Abstract The photoluminescence spectrum of PbWO 4 is composed of blue and green bands, previously attributed to the regular WO 4 group and to the defect-related WO 3 group, respectively. Untill now only green emission was observed in the thermostimulated luminescence (TSL) above 77 K. Investigation of the TSL spectra starting from 20 K indicates that the blue band, being definitely present at least in the 28 K TSL peak, is also due to recombination emission at defect sites.
Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)2PbI4 Perovskite Thin Films: Implications fo…
2021
An outstanding potentiality of layered two-dimensional (2D) organic–inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundament…
Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time…
2008
The article describes an experimental method that allows to estimate the inhomogeneous and homogeneous linewidths of the photoluminescence band of a point defect in an amorphous solid. We performed low temperature time-resolved luminescence measurements on two defects chosen as model systems for our analysis: extrinsic Oxygen Deficient Centers (ODC(II)) in amorphous silica and F+ 3 centers in crystalline Lithium Fluoride. Measurements evidence that only defects embedded in the amorphous matrix feature a dependence of the radiative decay lifetime on the emission energy and a time dependence of the first moment of the emission band. A theoretical model is developed to link these properties to…
Fast Luminescence Studies of NaLaF4: Pr3+ Glass Ceramics
2021
Cathodoluminescence (CL) emission and photoluminescence (PL) emission and excitation spectra of $16\mathbf{Na}2\mathbf{O}-9\mathbf{NaF}-5\mathbf{LaF}_{3}-7\mathbf{Al}_{2}\mathbf{O}_{3}-63\mathbf{SiO}_{2}$ (mol%) activated with 3% $\mathbf{PrF}_{3}$ , hereinafter referred to as $\mathbf{NaLaF}_{4}:\mathbf{Pr}_{9}^{3+}$ have been investigated. In particular, CL spectra were measured with time resolution after excitation with a 120 keV electron beam. The characteristic Pr3+ ion emission with fast decay times $\tau_{1}=1.77$ ns and $\tau_{2}=52.97$ ns at peak intensity at 406 nm were observed, which correspond well to the emission bands of the $\mathbf{Pr}^{3+}$ ion in other luminescent materia…
Study of the germanium luminescence in silica: from non-controlled impurity to germano-silicate core of telecommunication fiber preforms
2003
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…
Luminescence study of defects in synthetic as-grown and HPHT diamonds compared to natural diamonds
2005
The optically active defects in as-grown, high-pressure high-temperature-treated (HPHT), boron-doped, and synthetic diamonds (SD) grown with a nitrogen-getter, as well as of natural diamonds (ND), were characterized by absorption and luminescence spectroscopies using different excitation sources. The laser-excited photoluminescence (PL) spectra of SDs show numerous sharp lines characteristic for nickel-related centers, whereas NDs yield mainly broad PL bands. The emission from the nickel-related defects in NIR range increases and the maxima of the bands shift to lower energies with increasing temperature. Under UV and electron beam excitation, the yellow synthetic diamonds display green lum…
Infrared and optical observations of the newly identified Be/X-ray binary LSI + 61 235
1993
Observational (IR) and optical data are presented of the newly discovered Be/X-ray binary system LSI + 61° 235, taken over the period 1991 August – 1992 May. Though the IR shows little evidence for any changes, the optical Hα spectrum has undergone substantial modification. Combination of optical photometric measurements with the IR photometry allows the overall spectrum to be investigated and the existence of the Be star’s circumstellar disc to be directly confirmed.
The cool Galactic R Coronae Borealis variable DY Persei
2005
Results of first CCD photometry during the recent deep light decline, and high-resolution spectroscopy, are presented for DY Persei. The spectra show variable blueshifted features in the sodium D lines. The C lines are strong whereas neutron- capture elements are not enhanced. The isotopic 13 CN(2, 0) lines relative to 12 CN are of similar strength with those for the carbon star U Hya. All these confirm the RCB nature of DY Per and the existence of ejected clouds. At least two clouds are revealed at −197.3 and −143.0 km s −1 . A star was detected about 0. 4t o the west and 2 . 5 to the north from DY Per. This anonymous companion, with observed colour indices (B − V) = 0.68 and (V − R) � 1…
Advanced Hardware and Software for the Upgrade of Mirror/Prisma Monochromator SPM-2 (Carl Zeiss Jena) for the Measurements of Basic Spectroscopic Pro…
2021
Today's digital electronics and fast computers allow the efficiently processing of large volumes of spectroscopic information, which means the opportunity to reuse and upgrade monochromator with sophisticated optical and mechanical systems being designed and used in the middle of the last century. Particular interest is towards high-resolution prism monochromator. We used such an approach to computerize manual operations of universal mirror monochromator SPM-2, which has changeable quartz, glass, NaCl and KBr crystal prisms. SPM-2 was produced by VEB Carl Zeiss JENA in the early sixties of the last century (in former GDR), and its advanced features were widely used [1]. The current interest…