Weak thermal quenching of the luminescence in the Ca3Sc2Si3O12:Ce3+ garnet phosphor

Abstract

We report results of the luminescence properties of the three garnet type phosphors Ce³⁺-doped Ca₃Sc₂Si₃O₁₂ (CSSO:Ce³⁺), Sr₃Y₂Ge₃O₁₂ (SYG:Ce³⁺) and Y₃Al₅O₁₂ (YAG:Ce³⁺), investigated using optical spectroscopy techniques and vacuum referred binding energy (VRBE) diagram analysis. By monitoring the temperature dependence of the luminescence decay time we establish an excellent, intrinsic, thermal stability of luminescence in CSSO:Ce³⁺, with a nearly constant decay time (≈60 ns) up to, at least, T = 860 K. In comparison, SYG:Ce³⁺ and YAG:Ce³⁺ exhibit a significant reduction of the luminescence decay time upon heating, starting at around T = 280 K and T = 550 K, respectively, suggesting a lower internal thermal stability of luminescence in these two garnet phosphors. These findings are supported by the energy separation between the Ce³⁺ 5d₁ level and the conduction band (CB) of the respective hosts, which are found at 1.36 eV (CSSO:Ce³⁺), 0.45 eV (SYG:Ce³⁺), and 1.17 eV (YAG:Ce³⁺), respectively, as predicted by their VRBE diagrams. The performance of CSSO:Ce³⁺ was evaluated by applying the phosphor on a blue InGaN LED. The system shows a luminous efficacy of optical radiation of 243 lm W⁻¹ and a linear response with increasing applied voltage, suggesting it is a highly promising phosphor for future technological applications, particularly at high temperature operating environments.