This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce³⁺-doped Y_3−xCa_xAl_5−ySi_yO₁₂ 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 Y_3−xCa_x Al_5−ySi_yO₁₂: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 Y_3−xCa_xAl_5−ySi_yO₁₂: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 Y_3−xCa_xAl_5−ySi_yO₁₂: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 Y_3−xCa_xAl_5−ySi_yO₁₂ 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.

Ce³⁺ doped Al₂O₃-YAG eutectics were successfully grown by the horizontal directional crystallization method. The crystallization rate of eutectic growth was changed in the 1–7.5 mm/h range at a growth temperature of 1835 ℃. The microstructure of eutectic samples was investigated using scanning electron microscopy and X-ray microtomography. The intrinsic morphology of eutectic represents the stripe-like channel structure with a random distribution of the garnet Y₃Al₅O₁₂ (YAG) and Al₂O₃ (sapphire) phases. The content of these phases in the stripes changes in the 52.9–55.3% and 46.1–47.1% ratios, respectively, depending on the growth rate of the crystallization of the eutectic samples. The luminescent properties of the eutectic demonstrated the dominant Ce³⁺ luminescence in the garnet phase. The luminescence of the Ce³⁺ ions in Al₂O₃ has also been observed and the effective energy transfer processes between Ce³⁺ ions in the Al₂O₃ and YAG garnet phases were revealed under high-energy excitation and excitation in the UV Ce³⁺ absorption bands of sapphire. The phosphor conversion properties and the color characteristics (Al₂O₃-YAG):Ce eutectic with different thicknesses were investigated under excitation by a blue LED. We have also tested the prototypes of white LEDs, prepared using a blue 450 nm LED chip and (Al₂O₃-YAG):Ce eutectic photoconverters with 0.15 to 1 mm thicknesses. The results of the tests are promising and can be used for the creation of photoconverters for high-power white LEDs.

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.

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.

This work presents a comprehensive study of the structural, luminescent, and photoconversion properties of epitaxial composite phosphor converters based on single crystalline films of Ce³⁺-activated Ca_2−xY_1+xMg_1+xSc_1−xSi₃O₁₂:Ce (x = 0–0.25) (CYMSSG:Ce) garnet, grown using the liquid phase epitaxy (LPE) method on single-crystal Y₃Al₅O₁₂ (YAG) and YAG:Ce substrates. The main goal of this study is to elucidate the structure–composition–property relationships that influence the photoluminescence and photoconversion efficiency of these film–substrate composite converters, aiming to optimize their performance in high-power white light-emitting diode (WLED) applications. Systematic variation in the Y³⁺/Sc³⁺/Mg²⁺ cationic ratios within the garnet structure, combined with the controlled tuning of film thickness (ranging from 19 to 67 µm for CYMSSG:Ce/YAG and 10–22 µm for CYMSSG:Ce/YAG:Ce structures), enabled the precise modulation of their photoconversion properties. Prototypes of phosphor-converted WLEDs (pc-WLEDs) were developed based on these epitaxial structures to assess their performance and investigate how the content and thickness of SCFs affect the colorimetric properties of SCFs and composite converters. Clear trends were observed in the Ce³⁺ emission peak position, intensity, and color rendering, induced by the Y³⁺/Sc³⁺/Mg²⁺ cation substitution in the film converter, film thickness, and activator concentrations in the substrate and film. These results may be useful for the design of epitaxial phosphor converters with tunable emission spectra based on the epitaxially grown structures of garnet compounds.