Search results for " Luminescence"
showing 10 items of 159 documents
The search for defects in undoped SrAl2O4 material
2019
This research project was supported financially by ERDF Project No: Nr.1.1.1.1/16/A/182 .
Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride
2018
We present an \textit{ab initio} method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN which has an indirect band gap and is known for its strong luminescence in the UV range. We first analyse the excitons at the wave vector $\overline{q}$ of the indirect gap. The coupling of these excitons with the various phonon modes at $\overline{q}$ is expressed in terms of a product of the mean square displacement of the atoms and the second derivative of the optical response function with respect to atomic displacement along the phonon eigenvectors. The derivatives are calculated numerically with a fin…
Luminescence mechanisms of defective ZnO nanoparticles.
2016
ZnO nanoparticles (NPs) synthesized by pulsed laser ablation (PLAL) of a zinc plate in deionized water were investigated by time-resolved photoluminescence (PL) and complementary techniques (TEM, AFM, μRaman). HRTEM images show that PLAL produces crystalline ZnO NPs in wurtzite structure with a slightly distorted lattice parameter a. Consistently, optical spectra show the typical absorption edge of wurtzite ZnO (Eg = 3.38 eV) and the related excitonic PL peaked at 3.32 eV with a subnanosecond lifetime. ZnO NPs display a further PL peaking at 2.2 eV related to defects, which shows a power law decay kinetics. Thermal annealing in O2 and in a He atmosphere produces a reduction of the A1(LO) Ra…
Structure and Phase Changes in Natural and Synthetic Magnesium Aluminum Spinel
2015
Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E>0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n>1) has to be more disordered, since in addition to the site exchange …
Luminescence of natural α-quartz crystal with aluminum, alkali and noble ions impurities
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1–0289 .
UV light induced luminescence processes in AlN nanotips and ceramics
2005
UV induced luminescence properties of AlN (Eg = 6.2 eV) have been studied for AlN nanotips and AlN ceramics, using methods of photoluminescence, optically stimulated luminescence and thermoluminescence. In both types of objects the main luminescence band, which appears in prompt and stimulated emission spectra around 400 nm, arises due to presence of oxygen-related defects. The main difference between AlN nanotips and AlN ceramics is observed in excitation spectra and TL properties. Basing on the experimental results it is assumed that several different energy transfer mechanisms occur in AlN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of annealing treatment on the persistent luminescence of Y3Al2Ga3O12:Ce3+,Cr3+,Pr3+ ceramics
2020
Abstract The Y3Al2Ga3O12:Ce3+,Cr3+,Pr3+ (YAGG) persistent luminescent ceramics were sintered in static air (without airflow) and followed by hot isostatic pressing (HIP) treatment. The low aggregated and relatively narrow particle-size distributed starting powders, with the particle size of about 50 nm, were synthesized by using Pechini method and then annealed at 900 °C for 16 h in static air. Compared to nano-phosphors, the ceramics exhibited more intense and longer persistent luminescence (PersL). The photoluminescence and PersL spectra were found to have a similar shape, indicating that the emitting centers for photoluminescence and PersL processes were same. The intense Ce3+ and Cr3+ b…
Effect of Ce3+ concentration on persistent luminescence of YAGG:Ce3+,Cr3+,Nd3+ nanophosphors obtained by the co-precipitation method
2020
Abstract Synthesis of Y3Al2Ga3O12 garnet (YAGG) nanophosphors co-doped with Ce3+, Cr3+, and Nd3+ ions by co-precipitation is reported. The effect of Ce3+ concentration on the structure of garnet and on optical properties including persistent luminescence was investigated. The X-ray diffraction measurements showed that single garnet phase was obtained. The contraction of the crystallites size was observed with increasing the cerium concentration. The combined emission of three used co-dopants together allows to extend persistent luminescence spectral range. The photoluminescence, excitation and persistent luminescence spectra were collected and the optimal Ce3+ concentration for the highest …
Luminescence of localized states in oxidized and fluorinated silica glass
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.
Synthesis of multi-color luminescent ZnO nanoparticles by ultra-short pulsed laser ablation
2020
Abstract Crystalline ZnO nanoparticles (NPs) are synthesized by ultra-short femtosecond (fs) pulsed laser ablation (PLA) of a zinc plate in deionized water, and are investigated by optical absorption and time resolved luminescence spectra in combination with the morphology and structure analysis. The comparison with previous experiments based on short nanosecond (ns) PLA highlights that pulse duration is a crucial parameter to determine the size and the optical properties of ZnO NPs. While short PLA generates NPs with average size S ‾ of ~ 30 nm, ultrashort PLA allows to achieve much smaller NPs, S ‾ ⩽ 10 nm, that evidence weak quantum confinement effects on both the absorption edge and th…