High-Sensitivity and High-Precision Near-Infrared Luminescence Thermometry Using Mn5+-Activated Sr5(VO4)3Cl and Ba5(VO4)3Cl-Based Phosphors

Abstract A series of near-infrared-emitting materials of composition A5(V1–xO4)3Cl:Mnx (A = Ca2+, Sr2+, Ba2+; x = 0.00, 0.01, 0.03, 0.05) were prepared and characterized by X-ray diffraction, solid-state NMR, and room-temperature luminescence measurements. Two candidates (Sr5(V0.97O4)3Cl:Mn0.03 and Ba5(V0.97O4)3Cl:Mn0.03) were selected for detailed evaluation as luminescence thermometers. Three single-parameter luminescence thermometry methods (based on relative intensities, band positions, and band widths) were explored. Through multiparametric thermometry, we show that Sr5(V0.97O4)3Cl:Mn0.03 has remarkable performance parameters at physiological temperature (308 K): temperature relative sensitivity Sr = 3.14% K–1 and temperature resolution of 0.042 K. The multiparametric approach gives even better accuracy than the best individual readout (that based on luminescence intensity ratio, LIR), while retaining the exceptionally good temperature determination precision of the best single-parametric method (that based on bandwidth). Three different parameter-free full-spectrum luminescence thermometry methods were also applied, giving temperature readout accuracy values ranging from 0.03 to 0.08 K, while maintaining average resolution values of 0.07–0.08 and 0.07 K across the temperature range studied. These performance parameters – coupled with the remarkable brightness in the second biological window (photoluminescence quantum yield of 47%) and the thermal stability at both long-range and local-structure length-scales demonstrated by variable-temperature X-ray diffraction and solid-state NMR, respectively─make Sr5(V0.97O4)3Cl:Mn0.03 a very promising candidate for luminescence thermometry at physiological temperatures.