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.