Single Crystalline Films of Ce-Doped YMgSiAlO 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 Ce-doped YMgSiAlO 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 YMgSiAlO:Ce SCFs were examined in comparison with YAlO:Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg and Mg-Si codopants also showed a photocurrent that increased with rising Mg and Si concentrations. Mg excess was systematically present in as-grown YMgSiAlO: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 Ce ions as compensators for the Mg excess. The Ce dopant recharged to the Ce state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N + 5%H). 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 YMgSiAlO:Ce SCFs provide evidence for Ce multicenter formation and the presence of an energy transfer between various Ce multicenters. The Ce multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg and the tetrahedral positions by Si. In comparison with YAG:Ce SCF, the Ce luminescence spectra of YMgSiAlO:Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of YMgSiAlO:Ce garnets as a result of Mg and Si alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.