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

Abstract

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 Cr^{3+ 2}E 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).