The effects of temperature and impurity phases on the luminescent properties of Ce³⁺-doped Ca₃Sc₂Si₃O₁₂ garnet

The luminescent properties of Ce³⁺ ions in Ca₃Sc₂Si₃O₁₂ were studied in the temperature range of 77–800 K. It was found, for the first time, that at 77 K zero-phonon lines of 5d↔4f transitions and vibronic structure are distinctly observed in the Ce³⁺ emission and excitation spectra. The decay time of the Ce³⁺ emission in Ca₃Sc₂Si₃O₁₂ was found to be nearly constant (~ 71 ns) up to 700 K. This indicates that the thermal quenching of the Ce³⁺ emission in Ca₃Sc₂Si₃O₁₂ starts at high temperatures (≥ 750 K). The decrease of the Ce³⁺ integrated emission intensity (upon direct excitation of the lowest-energy Ce³⁺ 5d₁ state) with increasing temperature in the range of 350–700 K, often attributed to the thermal quenching, probably arises from temperature changes of 4f→5d₁ transition absorption strength. It was shown that typical impurity phases (β-Ca₂SiO₄, CaSiO₃, CeO₂) can cause competing ^parasitic absorption in the 250–380 nm range and they are expected to be responsible for variations in the luminescence excitation and diffuse-reflection spectra reported in the literature for Ce³⁺-doped Ca₃Sc₂Si₃O₁₂. A comparison with literature data on Ce³⁺-doped aluminum garnets (Y₃Al₅O₁₂ and Lu₃Al₅O₁₂) is also made.