Facile pechini synthesis of Sr3Y2Ge3O12:Bi3+/Eu3+ phosphors with tunable emissions and energy transfer for WLEDs

Abstract

A series of Sr3Y2Ge3O12 (SYGO), SYGO:Bi3+, SYGO:Eu3+ and SYGO:Bi3+/Eu3+ phosphors were synthesized by a facile pechini type sol-gel method. X-ray diffraction patterns exhibited a characteristic cubic lattice structure with a space group of la3¯d(230) after annealing at 1200 °C for 8 h. The morphological properties of the SYGO host lattice were studied by a field-emission scanning electron microscope, which displayed nearly spherical-shaped particles. Under ultraviolet (UV) or near-UV excitations, the SYGO:Bi3+ phosphors showed the blue emission of Bi3+ (3P1 → 1S0) at 467 nm and the SYGO:Eu3+ phosphors exhibited orange red emission of Eu3+ (5D0 → 7F1) at 594 nm, respectively. The energy transfer process was investigated in between the Bi3+ and Eu3+ ions by the wide spectral overlap of Bi3+ emission spectrum and Eu3+ excitation spectrum. The efficient energy transfer phenomenon from Bi3+ to Eu3+ ions was studied by adjusting the Eu3+ ion concentration in SYGO:Bi3+/Eu3+ phosphors and it was strongly confirmed by their luminescence decay curves. The critical distance was calculated for the energy transfer process from Bi3+ to Eu3+ ions due to the concentration quenching effect and it was further demonstrated to be a resonance type of quadrupole-quadrupole interactions. The obtained photoluminescence results revealed tunable emissions from blue to cool white, depending on the Eu3+ ion concentration. Furthermore, the thermal properties and quantum yield of the optimized cool white-light emitting SYGO:0.02Bi3+/0.05Eu3+ phosphor sample were studied and it exhibited good thermal stability with 20.5% quantum yield. Commission International de I'Eclairage chromaticity coordinates were calculated for all the prepared samples. Therefore, all these results indicate that the SYGO:0.02Bi3+/0.05Eu3+ is a promising phosphor for the application of white light-emitting diodes.