Tunable emission of Li4SrCaSi2O4-yN2y/(3):Eu2+ phosphors based on anion substitution induction for WLEDs and optical thermometry

Polychromatic emission can be achieved by controlling the distribution of the rare earth activator in multi-cation lattices, which can be used in the fields of white light LED and fluorescence temperature sensing. However, it is still a challenge to control their distribution and location of the target site in a given host material because the distribution of the rare earth activator is uncertain. In this paper, we have chosen Li4SrCa(SiO4)(2) as the multi-cation site host and induced the distribution of Eu2+ ions between different cation sites through anion substitution, for the first time, to regulate the luminescence characteristics of a series of Li4SrCaSi2O8-yN2y/3:Eu2+ phosphors. In Li4SrCa(SiO4)(2):Eu2+ phosphors, the substitution of O2- by N3- triggered a distinct ordered to disordered structure transition of the SiO4 tetrahedron and induced the remote distribution of the Eu2+ activator, which was verified through the analysis of the XRD, EPR, FT-IR and fluorescence spectra. Due to the location of Eu2+ ions in different cation sites (Eu-Sr(2+) and Eu-Ca(2+)), two distinguishable emission peaks with tunable color emissions and different responses to temperature were realized. The white LED that utilized blue-orange-emitting Li4SrCaSi2O4N8/3:Eu2+ and green-emitting BaSi2O2N2:Eu2+ (500 nm) displayed an outstanding color rendering index (R-a) of 85.1. Based on the fluorescence intensity ratio (FIR) technique, an optical temperature measurement mechanism was hypothesized and studied in the temperature range of 293-473 K. The highest S-a of the material was 0.086 K-1, and S-r was 1.76% K-1 based on the FIR detection technology, revealing obviously better than most inorganic optical temperature-measuring materials reported before. Our work indicates that Li4SrCaSi2O8-2yN4y/3:Eu2+ is a promising material for application in White LEDs and optical thermometers.