A ratiometric and lifetime-based luminescent thermometer exploiting the Co3+ luminescence in CaAl2O4:Co3+ and CaAl2O4:Co3+,Nd3+

Abstract

The growing interest in luminescence thermometry and the desire to improve the thermometric properties of luminescent thermometers prompt the search for new solutions including new materials and types of luminescent ions. In this work, we present for the first time a systematic study verifying the application potential of materials doped with Co³⁺ ions in luminescence thermometry. It was shown that the luminescence intensity of the emission band localized at 800 nm associated with a spin-forbidden ³T_1(g)(H) → ¹A_1(g)(I) electronic transition of Co³⁺ ions exhibits strong temperature quenching accompanied by a strong shortening of the lifetime of the ³T_1(g)(H) level upon temperature increase. This has enabled the development of a ratiometric luminescent thermometer in CaAl₂O₄:Co³⁺,Nd³⁺, particularly effective at temperatures around room temperature (250 K < T < 350 K). It is characterized by a relative sensitivity of S_R of 1.86% K⁻¹ at 263 K and a thermometer based on a luminescence lifetime of S_R of 2.36% K⁻¹ at 349 K. It is shown that changing the structure from hexagonal to monoclinic CaAl₂O₄ does not change the spectral position of the emission band but increases the temperature quenching behavior of the Co³⁺ luminescence.