A CaMgZnGaO:Bi/Mn phosphor: energy transfer enables tuneable colour emission and high sensitivity in optical thermometry.

Recent advancements in optical thermometry utilizing fluorescence intensity ratio (FIR) technology have attracted tremendous attention in real-time temperature measurements due to its numerous advantages, such as high sensitivity. In this work, we rationally designed an FIR-type thermometer by utilizing the distinctive thermal responses of blue and far-red emission from Bi and Mn activators, respectively. To achieve a broad range of FIR values, we first optimized the blue emission of CaMgZnGaO:0.05Bi (CMZGO:0.05Bi) through Zn-to-Mg substitution and then utilized Bi/Mn co-doping into the optimal composition to realize dual emission. The blue emission of CMZGO:0.05Bi was improved significantly, which is associated with complex spectroscopic red and blue shifts due to the competitive effect of crystal field splitting and centroid shift for Bi emitters. Additionally, Bi/Mn-co-doped CMZGO:0.05Bi/Mn phosphors exhibit tuneable colour emission from blue to deep-red, arising from an increased energy transfer efficiency from Bi to Mn upon increasing the Mn content. Benefitting from this energy transfer, Bi and Mn activators demonstrate severe thermal quenching and high thermal stability, respectively, thereby resulting in a high relative sensitivity () value of 1.64% K to temperature measurement. This value surpasses that of most Bi/Mn- and Bi/Eu-co-doped optical thermometers, implying the promising application potential of CMZGO:0.05Bi/0.001Mn as an optical thermometer.