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

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 T-3(1(g))(H) -> (1)A(1(g))(I) electronic transition of Co3+ ions exhibits strong temperature quenching accompanied by a strong shortening of the lifetime of the T-3(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.