Single Crystalline Films of Ce3+-Doped Y3MgxSiyAl5-x-yO12 Garnets: Crystallization, Optical, and Photocurrent Properties

This research focuses on LPE growth, and the examination of the optical and photovoltaic properties of single crystalline film (SCF) phosphors based on Ce³⁺-doped Y₃Mg_xSi_yAl_5-x-yO₁₂ garnets with Mg and Si contents in x = 0-0.345 and y = 0-0.31 ranges. The absorbance, luminescence, scintillation, and photocurrent properties of Y₃Mg_xSi_yAl_5-x-yO₁₂:Ce SCFs were examined in comparison with Y₃Al₅O₁₂:Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg²⁺ and Mg²⁺-Si⁴⁺ codopants also showed a photocurrent that increased with rising Mg²⁺ and Si⁴⁺ concentrations. Mg²⁺ excess was systematically present in as-grown Y₃Mg_xSi_yAl_5-x-yO₁₂:Ce SCFs. The as-grown SCFs of these garnets under the excitation of α-particles had a low light yield (LY) and a fast scintillation response with a decay time in the ns range due to producing the Ce⁴⁺ ions as compensators for the Mg²⁺ excess. The Ce⁴⁺ dopant recharged to the Ce³⁺ state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N₂ + 5%H₂). Annealed SCF samples exhibited an LY of around 42% and similar scintillation decay kinetics to those of the YAG:Ce SCF counterpart. The photoluminescence studies of Y₃Mg_xSi_yAl_5-x-yO₁₂:Ce SCFs provide evidence for Ce³⁺ multicenter formation and the presence of an energy transfer between various Ce³⁺ multicenters. The Ce³⁺ multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg²⁺ and the tetrahedral positions by Si⁴⁺. In comparison with YAG:Ce SCF, the Ce³⁺ luminescence spectra of Y₃Mg_xSi_yAl_5-x-yO₁₂:Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of Y₃Mg_xSi_yAl_5-x-yO₁₂:Ce garnets as a result of Mg²⁺ and Si⁴⁺ alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.

Micropowder Ca2YMgScSi3O12:Ce Silicate Garnet as an Efficient Light Converter for White LEDs

This work is dedicated to the crystallization and luminescent properties of a prospective Ca2YMgScSi3O12:Ce (CYMSSG:Ce) micropowder (MP) phosphor converter (pc) for a white light-emitting LED (WLED). The set of MP samples was obtained by conventional solid-phase synthesis using different amounts of B2O3 flux in the 1-5 mole percentage range. The luminescent properties of the CYMSSG:Ce MPs were investigated at different Ce3+ concentrations in the 1-5 atomic percentage range. The formation of several Ce3+ multicenters in the CYMSSG:Ce MPs was detected in the emission and excitation spectra as well as the decay kinetics of the Ce3+ luminescence. The creation of the Ce3+ multicenters in CYMSSG:Ce garnet results from: (i) the substitution by the Ce3+ ions of the heterovalent Ca2+ and Y3+ cations in the dodecahedral position of the garnet host; (ii) the inhomogeneous local environment of the Ce3+ ions when the octahedral positions of the garnet are replaced by heterovalent Mg2+ and Sc3+ cations and the tetrahedral positions are replaced by Si4+ cations. The presence of Ce3+ multicenters significantly enhances the Ce3+ emission band in the red range in comparison with conventional YAG:Ce phosphor. Prototypes of the WLEDs were also created in this work by using CYMSSG:Ce MP films as phosphor converters. Furthermore, the dependence of the photoconversion properties on the layer thickness of the CYMSSG:Ce MP was studied as well. The changes in the MP layer thickness enable the tuning of the white light thons from cold white/daylight to neutral white. The obtained results are encouraging and can be useful for the development of a novel generation of pcs for WLEDs.

Novel composite color converters based on Tb1.5Gd1.5Al5O12:Ce single crystalline films and Y3Al5O12:Ce crystal substrates

The structural, luminescence and photoconversion properties of composite color converters based on Tb1.5Gd1.5AG:Ce single crystalline films, grown by the liquid phase epitaxy method onto YAG:Ce single crystal substrates, are investigated.

Crystallization and Investigation of the Structural and Optical Properties of Ce3+-Doped Y3−xCaxAl5−ySiyO12 Single Crystalline Film Phosphors

This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce3+-doped Y3−xCaxAl5−ySiyO12 garnet, where the content of Ca2+ and Si4+ cations varied in the x = 0.13–0.52 and y = 0.065–0.5 ranges, respectively. The SCF samples were grown using the liquid phase epitaxy technique onto Y3Al5O12 substrates from the melt solution with equimolar Ca and Si content using PbO-B2O3 flux. However, the Ca and Si concentration in Y3−xCax Al5−ySiyO12:Ce SCFs is not equal: the Ca2+ content was systematically larger than that of Si4+, and the Ca2+ excess is compensated for by the Ce4+ ion formation. The absorption, scintillation, and luminescent properties of Y3−xCaxAl5−ySiyO12:Ce SCFs with different Ca/Si concentrations were investigated and compared with the sample of YAG:Ce SCF. Due to the creation of Ce4+ ions, the as-grown Y3−xCaxAl5−ySiyO12:Ce SCFs show relatively low light yield (LY) under α–particle excitation but a fast scintillation response with a decay time in the ns range. After SCF annealing in the reducing (N2 + H2) atmosphere at T > 1000 °C, the recharging of Ce4+→Ce3+ ions occurs. Furthermore, the samples annealed at 1300 °C SCF possess an LY of about 40% in comparison with the reference YAG:Ce SCF and scintillation decay kinetics much closer to that of the SCF counterpart. Due to Ca2+ and Si4+ alloying, the Ce3+ emission spectra in Y3−xCaxAl5−ySiyO12 SCFs are extended to the red range in comparison with the spectra of YAG:Ce SCF. Such an extension is caused by the Ce3+ multicenter formation at the substitutions of both Y3+ and Ca2+ dodecahedral positions in the hosts of these mixed garnets.

Overview of S(T)EM electron detectors with garnet scintillators: Some potentials and limits

The paper is focused on a complete configuration and design of a scintillation electron detector in scanning electron and/or scanning transmission electron microscopes (S(T)EM) with garnet scintillators. All processes related to the scintillator and light guide were analyzed. In more detail, excitation electron trajectories and absorbed energy distributions, efficiencies and kinetics of scintillators, as well as the influence of their anti-charging coatings and their substrates, assigned optical properties, and light guide efficiencies of different configurations were presented and discussed. The results indicate problems with low-energy detection below 1 keV when the scandium conductive coating with a thickness of only 3 nm must be used to allow electron penetration without significant losses. It was shown that the short rise and decay time and low afterglow of LuGdGaAG:Ce liquid-phase epitaxy garnet film scintillators guarantee a strong modulation transfer function of the entire imaging system resulting in a contrast transfer ability up to 0.6 lp/pixel. Small film scintillator thicknesses were found to be an advantage due to the low signal self-absorption. The optical absorption coefficients, refractive indices, and the mirror optical reflectance of materials involved in the light transport to the photomultiplier tube photocathode were investigated. The computer-optimized design SCIUNI application was used to configure the optimized light guide system. It was shown that nonoptimized edge-guided systems possess very poor light guiding efficiency as low as 1%, while even very complex optimized ones can achieve more than 20%.