Large temperature sensitivity of optical emission via synergy of Raman and photoluminescence effects in BaTiO3-based phosphor

The growing interest in luminescence-based optical thermometry in recent years is motivated by the prospect of designing phosphor materials capable of exhibiting large temperature sensitivity of the emission spectrum. The prevalent material design strategies predominantly rely on ascertaining temperature sensitivity using fluorescence intensity ratio (FIR) of the Stark lines in the photoluminescence (PL) emission spectrum of rare-earth(s) doped materials. This approach has yielded temperature sensitivity in the range 0-5% . Here we propose a new strategy for achieving high temperature sensitivity by considering a twin combination of Raman and PL spectrum of the phosphor material, and by introducing Raman-PL-intensity ratio (RPIR) as a parameter for measuring relative temperature sensitivity(S_r). The effectiveness of this concept is demonstrated on Eu/Er-doped BaTiO₃ wherein a large S_r range (-3 % to +6 %) and large color tuning (red to green) was achieved by exploiting the mechanisms which resulted in a contrasting effect of temperature on Raman and the PL part of the total spectra.