Search results for "EXCITATION"
showing 10 items of 1290 documents
Defect Luminescence of LiBaF3 Perovskites
2000
Blue and red luminescence of undoped LiBaF3 crystals was studied. A broad, isotropic photoluminescence band centered at 410 nm can be excited by 210 nm — 275 nm light in as grown crystals. After X-irradiation at RT a new narrower, anisotropic luminescence band appears at 425 mn which has an additional excitation band at 290 nm. The X-irradiation also creates the F- type centres and anisotropic centres with an absorption band at 630 nm and a luminescence band at 700 nm. No F- centre luminescence is observed. All the other centres mentioned act as radiative recombination centers as well. It is speculated that the origin of the blue luminescence is due to oxygen defects and that the red lumine…
Temperature dependence of O2 singlet photoluminescence in silica nanoparticles
2013
Abstract The near infrared singlet emission and photoluminescence lifetime of O 2 molecules embedded in silica nanoparticles are studied from room temperature down to 10 K. The area of the photoluminescence band under infrared excitation decreases for temperature above 100 K and the lifetime is shortened. These observations provide evidence of a thermally activated relaxation channel with activation energy of about 40 meV. This relaxation mechanism adds to the already known temperature independent electronic-to-vibrational coupling involving high energy vibrational modes of the host matrix or its impurities. The thermally activated process is suggested to consist in the breakage of the O 2 …
Valence-band splitting energies in wurtzite InP nanowires : Photoluminescence spectroscopy and ab initio calculations
2010
We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, r…
Isoelectronic series of oxygen deficient centers in silica: experimental estimation of homogeneous and inhomogeneous spectral widths
2008
We report nanosecond time-resolved photoluminescence measurements on the isoelectronic series of oxygen deficient centers in amorphous silica related to silicon, germanium and tin atoms, which are responsible of fluorescence activities at approximately 4 eV under excitation at approximately 5 eV. The dependence of the first moment of their emission band on time and that of the radiative decay lifetime on emission energy are analyzed within a theoretical model able to describe the effects introduced by disorder on the optical properties of the defects. We obtain separate estimates of the homogeneous and inhomogeneous contributions to the measured emission line width, and we derive homogeneou…
Luminescence and optical spectroscopy of charge transfer processes in solid solutions Ni Mg1−O and Ni Zn1−O
2016
Abstract In this work photoluminescence spectra for Ni c Mg 1− c O and Ni x Zn 1− x O solid solutions with the rock-salt crystal structure were obtained under synchrotron radiation excitation. Periodical peaks in the photoluminescence excitation spectrum of Ni c Mg 1− c O ( c =0.008) have been discovered for a wide-gap oxide doped with 3d impurities for the first time. They can be considered as LO phonon repetitions of the narrow zero phonon line resulted from the optical transitions into the p–d charge transfer exciton [d 9 h] state. A close coincidence in energy of different peculiarities in the optical absorption and photoluminescence excitation spectra for the Ni c Mg 1− c O and Ni x Zn…
Photoluminescence of Carbon Dots Embedded in a SiO2 Matrix
2016
Abstract We synthetized carbon dots by a pyrolitic method, and studied their photoluminescence in aqueous environment and upon trapping in a solid matrix. To this aim, we devised a facile procedure allowing to embed the dots in amorphous SiO2, without the need of any pre-functionalization of the nanoparticles, and capable of yielding a brightly photoluminescent monolith. Experimental data reveal a remarkable similarity between the emission properties of carbon dots in water and in SiO2, suggesting that the chromophores responsible of the photoluminescence undergo only weak interactions with the environment. Time-resolved photoluminescence data reveal that the typical photoluminescence tunab…
Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure
2014
International audience; In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10–50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is develo…
Recombination luminescence in aluminum nitride ceramics
2013
Photoluminescence (PL) and afterglow luminescence (AGL) produced by UV laser irradiation with varied intensity were studied in AlN ceramics in the 10–300 K temperature range. Luminescence spectra of AlN ceramics contain the UV–blue band built up of two components – the UV (3.18 eV) and Blue (2.58 eV) bands, which are presumably ascribed to recombination luminescence involving oxygen-related centers in the bulk and on the surface of AlN, correspondingly. It was found that position of the emission band maximum of AlN ceramics depends on such factors as excitation density, temperature, and delay time after excitation ceasing – in the case of AGL. In PL spectra, the excitation density growth pr…
Vertical stacks of small InAs/GaAs self-assembled dots: resonant and non-resonant excitation
2003
4 páginas, 2 figuras.-- PACS: 78.67.Hc; 73.21.La; 78.55.Cr.-- Proceedings of the International Conference on Superlattices, Nano-structures and Nano-devices ICSNN 2002.
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…