Highly efficient cyan-red emission in self-activated Sr9In(VO4)7:xEu3+ phosphors for applications in W-LEDs and optical thermometry

Optical thermometry based on fluorescence intensity ratio (FIR) has garnered much attention as it pushes beyond the limitations of traditional thermometers. Here, we present a new strategy for FIR thermometry using dual emissions from Sr9In(VO4)7:xEu3+ (SIVO:xEu3+) phosphors by a single activation. A series of color tunable SIVO:xEu3+ phosphors was successfully synthesized, and their luminescent properties were investigated. The phosphors emit broadband from VO43- groups as well as sharp emissions from Eu3+ ions upon ultraviolet excitation (320 nm) with high thermal stability and little to no concentration quenching of Eu3+. Meanwhile, the SIVO:0.8Eu3+ phosphor demonstrates a high quantum efficiency of 49%. The emitting color could be modulated from cyan to red via regulating the energy transfer efficiency from VO43- to Eu3+ ions by adjusting Eu3+concentration. A prototype LED device based on SIVO:xEu3+ phosphors produces a bright white light with low color temperatures (2967-3741 K) and high color rendering indices (87-88.4%). Moreover, optical thermometry measurement using fluorescence intensity ratio of VO43- and Eu3+ emissions demonstrated optimum absolute sensitivity and relative sensitivity of 0.0975 K-1 and 1.26% K-1, respectively. Regulating the energy transfer between the host and activator proved to be a feasible strategy to modulate the emission color and achieve optical thermometry in a single-phase phosphor. The reported results also provide insight to designing multifunctional materials for both White-LED (W-LED) and thermometry applications.