Modulating Thermometric Performance via Dopant Concentration and Morphology in a Luminescence Thermometer Exhibiting Dual Structural Phase Transitions

Expanding the operational range of luminescent thermometers that utilize thermally induced structural phase transitions in lanthanide-doped materials necessitates the exploration of novel host matrices with diverse thermal behaviors. In line with this objective, this study offers a comprehensive analysis of the temperature-dependent spectroscopic properties of Li3Sc2(PO4)3:Eu3+. The findings reveal that the studied material undergoes two reversible phase transitions: the γLT → α/β phase transition at approximately 160 K, followed by a β → γ HT transition around 550 K. These transitions are evidenced by notable alterations in the emission spectra and luminescence decay kinetics of Eu3+ ions. By employing an appropriate luminescence intensity ratio, the sensitivity was determined to be 7.8% K–1 at 160 K for 0.1% Eu3+ and 0.65% K–1 at 550 K for 0.5% Eu3+. Furthermore, the study demonstrates that the phase transition temperature in Li3Sc2(PO4)3:Eu3+ can be modulated through variations in dopant ion concentration and annealing conditions, which in turn influence the material’s morphology. These strategies enable the fine-tuning of thermometric performance in phase transition-based luminescent thermometers. To the best of our knowledge, this represents the first report in the literature of a luminescent thermometer exhibiting dual thermal operating ranges.