Synthesis and characterization of Eu3+-doped RbCaLa(VO4)2 phosphors and influence of temperature on fluorescence properties

Using the solid-state method, a novel optical thermometer, RbCaLa1-x(VO4)2:xEu3+ phosphor, was synthesized. Using X-ray diffraction, the phase of the RbCaLa1-x(VO4)2:xEu3+ was confirmed. The microstructure was then observed in the SEM pattern. To estimate the temperature, the fluorescence intensity ratio (FIR) method was used. To explain the temperature-sensing properties, the absolute (Sa) and relative (Sr) sensitivities were calculated. The maximum Sa and Sr values were then determined as 2.215% and 1.125% at 473 and 423 K, respectively. After multiple heating and cooling processes, the FIR value corresponding to each temperature stabilized. This indicated the reliability of the FIR fitting formula. Subsequently, to examine the formula's accuracy, multiple temperature points ranging from 298 to 473 K were selected. The results demonstrated that the measurement error could be controlled in ±1.1 K. The difference was considerably lesser in the high-temperature region (400–430 K), and the error was in ±0.21 K. Under UV light, the colors of the RbCaLa0.82(VO4)2:0.18Eu3+ phosphor and RbCaLa(VO4)2 matrix were somewhat different, and both considerably changed with temperature. All results showed that the Eu3+-doped RbCaLa(VO4)2 phosphor is a good candidate material as an optical temperature sensor and anti-counterfeiting coating.