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 T-4(2) and E-2 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 (T-4(2) -> (4)A(2)) and (E-2 -> (4)A(2)) is linear over 190-460 K in the Arrhenius plot, ensuring the reliability of the thermometer in this temperature range. The activation energy (Delta E) of the population process between the Cr3+ 2E and the T-4(2) 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).