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

A series of Sr(3)Y(2)G(e3)O(12)(SYGO),SYGO:Bi(3+,)SYGO:Eu3+ and SYGO:Bi3+/Eu3+ phosphors were synthesized facile pechini type sol-gel method. X-ray diffraction patterns exhibited a characteristic cubic lattice structure with a space group of l a(3) over bar d (230) after annealing at 1200 degrees 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+ (P-3(1) -> S-1(0)) at 467 nm and the SYGO: Eu3+ phosphors exhibited orange red emission of Eu3+ (D-5(0) -> F-7(1)) at 594 nm, respectively. The energy transfer process was investigated in between the Bi(3+)and Eu(3+)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 whitelight emitting SYGO: 0.02Bi(3+)/0.05Eu(3+) 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: 0.02Bi(3+)/ 0.05Eu(3+) is a promising phosphor for the application of white light-emitting diodes. (C) 2017 Elsevier B.V. All rights reserved.