A novel four-mode luminescent thermometry by employing cross-relaxation of upconversion fluorescence in Er3+-doped MgAlON transparent ceramics grain boundary

The upconversion fluorescence thermometry has been recognized as one of the most promising techniques for the temperature measurement and multi-mode fluorescence temperature sensing can improve the accuracy and widen the temperature range. Herein, a fluorescence thermometry was developed based on the MgAlON: Er3+ transparent ceramic. It was demonstrated that the enrichment of Er3+ in grain boundaries increased susceptibility to temperature variations of the cross-relaxation rate, which endowed the non-thermally coupled energy levels with temperature sensing properties and led to the multi-mode thermometric capability. A novel four-mode temperature sensor based on fluorescence intensity ratios (2H11/2/4S3/2 and 4F9/2/4S3/2) and fluorescent lifetimes (4F9/2 and 4S3/2) was realized in the temperature range of 180–500 K, which brought about the maximum absolute and relative sensitivities reached 0.0258 K−1 and 2.95% K−1, respectively. This work reveals that the MgAlON: Er3+ and the grain boundary functionalization of transparent ceramics could have potential applications for fluorescence thermometry.