Dual-mode optical ratiometric thermometry using Pr³⁺-doped NaSrGd(MoO₄)₃ phosphors with tunable sensitivity

Owing to some special superior features, luminescence ratiometric thermometry has acquired popularity, particularly dual excitation single emission (SBR) and single excitation dual emission (FIR). Nonetheless, it remains difficult to create ratiometric thermometry that can operate in multiple modes. The integration of FIR and SBR techniques paves the way for advancements in various fields, including industrial processes, environmental monitoring, and biomedical applications, where accurate temperature measurements are crucial for optimal performance and safety. In this work, we describe a way to measure temperature based on the light-induced fluorescence of Pr³⁺ in NaSrGd(MoO₄)₃ (NSGM). The optical properties were investigated by UV-visible absorption, PL, and PLE spectroscopy. On the one hand, the emission of Pr³⁺ exhibits varying temperature-dependent behavior upon 450 nm excitation. Thus, a thermometer based on the FIR between the Pr³⁺ levels has been generated, with the highest sensitivity of approximately 0.83% K^-1 over a wide temperature range of 290-440 K. Furthermore, the SBR luminescent thermometer was evaluated in the same temperature range. The effect of the Pr³⁺ concentration on red-emitting SBR luminescent thermometers was investigated in detail. The S_a and S_r values gradually increase, with the Pr³⁺ content reaching a maximum S_r value of 2.4% K^-1 at 413 K for the NSGM:10% Pr³⁺ phosphor. These results show that Pr³⁺ ions have the potential to be optically active centers for luminescent thermometer applications using FIR and SBR techniques. It is anticipated that the present work will inspire other researchers to employ multi-mode optical ratiometric thermometry more widely.