A reliable and stable ratiometric luminescence thermometer based on dual near-infrared emission in a Cr3+-doped LaSr2Ga11O20 phosphor

Luminescence Boltzmann thermometry is becoming one of the most trustworthy methods for locally measuring temperature in a noncontact mode. In this work, we report a comprehensive spectroscopic study of the Cr3+ electronic configuration in LaSr2Ga11O20. This phosphor shows distinct photoluminescence properties ascribed to the crystal field effect on Cr3+ emitters, which generates intense broadband and sharp near-infrared (NIR) emissions simultaneously from the 4T2 and 2E excited levels in a broad range of temperatures. Moreover, we investigate the spectroscopic response of the Cr3+-doped LaSr2Ga11O20 phosphor to a thermal stimulus by combining detailed experimental observations and theoretical analysis. The luminescence intensity ratio of two NIR emission transitions (4T2 → 4A2) and (2E → 4A2) is linear over 190–460 K in the Arrhenius plot, ensuring the reliability of the thermometer in this temperature range. The activation energy (ΔE) of the population process between the Cr3+ 2E and the 4T2 states is estimated to be 654 cm−1, which is in line with the value estimated by the intersection between the parabolas of the excited states using a configurational coordinate diagram. The results demonstrate high promise of this phosphor as a reliable ratiometric luminescence thermometer with high relative sensitivity (2.6%·K−1 at 190 K).