A reliable and stable ratiometric luminescence thermometer based on dual near-infrared emission in a Cr-doped LaSrGaO 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 Cr 3+ electronic configuration in LaSr 2 Ga 11 O 20 . This phosphor shows distinct photoluminescence properties ascribed to the crystal field effect on Cr 3+ emitters, which generates intense broadband and sharp near-infrared (NIR) emissions simultaneously from the 4 T 2 and 2 E excited levels in a broad range of temperatures. Moreover, we investigate the spectroscopic response of the Cr 3+ -doped LaSr 2 Ga 11 O 20 phosphor to a thermal stimulus by combining detailed experimental observations and theoretical analysis. The luminescence intensity ratio of two NIR emission transitions ( 4 T 2 → 4 A 2 ) and ( 2 E → 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 (Δ E ) of the population process between the Cr 3+ 2 E and the 4 T 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). A reliable and stable ratiometric luminescence thermometer with a high relative sensitivity (2.6%·K −1 at 190 K) is realized using a LaSr 2 Ga 11 O 20 :Cr 3+ phosphor.