Probing the multifunctionality of double layered perovskite NaGdMgTeO6:Eu3+ in ratiometric phosphor thermometry and solid-state lighting

Abstract

The present work deals with synthesis and optical properties of NaGdMgTeO6: x% Eu3+ (x = 2%, 4%, 6%, 8%, 10%, 12%, and 14%) double layered perovskite phosphors synthesized via conventional solid state ceramic route. X-ray diffraction profile along with Rietveld refinement reveals the single phase nature of the compounds. Further Raman and FTIR spectroscopy were carried out to deduce the structural modifications induced by the substitution of Eu3+ ions at Gd3+ site. A direct bandgap of 3.5 eV suggests that these phosphors can be efficiently excited using ultraviolet radiation. The compound can be efficiently excited by 265 nm and gives red emission at 615 nm corresponding to 5D0- 7F2 electric dipole transition of Eu3+ ions. The optimum doping concentration of Eu3+ is obtained as 8 mol% beyond which concentration quenching occurs. Thermal activation energy of the phosphor is evaluated as 0.2 eV. Thermal stability and other phosphor parameters show its potential application in solid state lighting. The relative temperature sensitivity and absolute sensitivity obtained by measuring fluorescence intensity ratio of 5D0→7F1 to 5D0→7F2 is 0.23%K-1 and 0.0072 K−1 respectively. Judd-Ofelt parameters were evaluated which are in good agreement with the results obtained from PL spectra. Judd-Ofelt theory is further extended to evaluate thermometric parameters by considering the emissions from 5D0 and 5D1 thermally coupled energy levels (TCLs) of Eu3+ ions. A good match is observed between thermometric parameters obtained by conventional method and Judd-Ofelt theoretical model. All the results suggested that NaGdMgTeO6: Eu3+ phosphors have potential applications in solid state lighting and optical thermometry.