Abstract
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.
Highlights
White light emitting diodes (WLEDs) are displacing traditional light sources due to their high luminous efficiency, energy saving ability, long lifetime, and environmental friendliness [1]
We present the results on the crystallization and investigation of the structural and optical properties of phosphors based on the single crystalline films (SCFs) of Ce3+-doped Y3−xCaxAl5−ySiyO12 garnet, where x = 0.13–0.52 and y = 0.065–0.5
From the microanalysis of the real content of the SCF samples (Table 1), we found the Ca2+ and Si4+ segregation coefficients in Y3−x Cax Al5−y Siy O12 :Ce SCF samples at nominal Ca (x) and Si (y) content in the melt solution in the 0.5–2 range (Figure 2)
Summary
White light emitting diodes (WLEDs) are displacing traditional light sources due to their high luminous efficiency, energy saving ability, long lifetime, and environmental friendliness [1]. We hope that the results of this pilot research will be useful for the development of luminescent materials for white LED converters, scintillators, cathodoluminescent screens, and other optoelectronic devices based on the epitaxial structures of Ca2+-Si4+-containing garnets, grown using the LPE method on doped or undoped substrates of garnet compounds. Five sets of optically perfect Y3−x Cax Al5−y Siy O12 :Ce SCF samples were crystallized using the LPE method on YAG substrates with an orientation close to (110) from the super cooling melt solution containing nominal equimolar (x = y) Ca and Si content in the. The XRD measurements were used for the characterization of the structural quality of Y3−x Cax Al5−y Siy O12 SCFs with different content x of Ca and Si cations, grown onto the YAG substrate with the (110) orientation and a lattice constant of 12.0069 Ȧ (Figure 3).
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