Investigations on structural and optical properties of Eu3+-activated Sr2GdNbO6 double-perovskite phosphors for solid-state lighting

Red-emitting phosphors with high quantum efficiency are required to develop high-performance white light-emitting diodes (WLEDs). Herein, we demonstrated a series of thermally stable, high-efficiency Eu3+ activated double perovskite Sr2GdNbO6 red phosphors synthesized via a high-temperature solid-state reaction method. A systematic investigation has been done into the structural, morphological and optical properties, including emission and excitation spectra, temperature-dependent luminescence, internal quantum efficiency (IQE), color purity and CIE chromaticity coordinates of the phosphors. The developed double perovskite oxide crystallizes in monoclinic form with a space group P2(1)/n. Under 392 nm excitation, the prepared phosphors exhibited intense red emission at about 613 nm attributed to the electric dipole transition (D-5(0) -> F-7(2)), with excellent color purity (95.56%) and high IQE (55%). The optimum doping concentration of Eu3+ was found to be 20 mol%, and the critical transfer distance of Eu3+ ion was calculated to be around 11 & Aring;. Furthermore, the Sr2Gd0.80NbO6:0.20Eu(3+) phosphor displayed significant thermal stability with a 0.18 eV activation energy, and the emission intensity at 423 K persisted around 77% of its original value at 300 K. The modification of the local environment around Eu3+ ions at low temperatures (similar to 80K) shift the energy levels and alter the probabilities of different emission processes, leading to the switching of emission from D-5(0) -> F-7(2) to D-5(0) -> F-7(1) transitions from Eu3+ activated Sr2GdNbO6 double-perovskite phosphors. These findings suggest that the Sr2GdNbO6:Eu3+ phosphors may find use in blue LED-based white light-emitting diodes (w-LEDs).