Tuning Temperature Sensitivity by Chemical Composition in Cr ³⁺ -doped (Y _{1– <i>x</i>} Gd _<i>x</i> ) ₃ (Al _{1– <i>y</i>} Ga _<i>y</i> ) ₅ O ₁₂

Remote temperature sensing using the temperature dependence of luminescence spectra or lifetimes of transition-metal and lanthanide ions is gaining popularity. For Cr3+, the temperature dependence of lifetime of emission from the thermally coupled 2E and 4T2 levels provides an easy and sensitive method to remotely measure temperature. The temperature range where the lifetime drops due to thermal population of the higher energy 4T2 level depends on the energy gap ΔE between the two levels. Here, we aim to vary ΔE for Cr3+-doped garnets (Y1–xGdx)3Al5O12 (0 ≤ x ≤ 0.8) and Y3(Al1–yGay)5O12 (0.2 ≤ y ≤ 1) and show how tuning of ΔE by chemical composition can be used to optimize the temperature-sensing performance in a specific temperature range. The variation in ΔE can be understood by a decrease in crystal-field splitting resulting from a lengthening of the Cr3+–O2– distance upon Al3+ ↔ Ga3+ or Y3+ ↔ Gd3+ substitution. Substitution of (Y,Gd) only gives a small variation of ΔE and shifts the temperature with the highest relative sensitivity Sr by less than 50 K, while (Al,Ga) substitution allows for tuning the temperature with the highest Sr from below 200 to around 300 K.