Luminescence and energy transfer of a single-phased phosphor Y2GeO5: Bi3+, Tm3+, Tb3+, Eu3+ for white UV LEDs

Abstract

A series of novel Y2GeO5: Bi3+, Tm3+, Tb3+, Eu3+ (YGO: Bi3+, Tm3+, Tb3+, Eu3+) phosphors were synthesized via high-temperature solid-state reaction. The structural, luminescent properties, as well as energy transfer mechanisms, in the phosphors were investigated in detail. The results indicate that all Bi3+, Tm3+, Tb3+ and Eu3+ ions substitute for Y3+ ions in host lattice of YGO without changing its crystal structure. Excitation and emission spectra were evaluated for the compounds. Energy transfer from Bi3+ to Tm3+, Tb3+/Eu3+ and Tb3+ to Eu3+ exist in phosphors YGO: Bi3+, Tm3+, Tb3+, Eu3+. Under the 308 nm excitation, the phosphor YGO: Bi3+, Tm3+, Tb3+ shows the characteristic transitions of Bi3+ (372 nm, 3P1, 0 → 1S0), Tm3+ (455 nm, 1D2→3F4), Tb3+ (544 nm, 5D4→7F5). However, Eu3+ is absent in the composition. Tunable colors from blue to green to red and white are achieved by varying excitation wavelength. The energy transfer from Bi3+ to Tm3+ is proved to be an electric dipole-dipole interaction. A white-light emission with the color coordinate (0.3146, 0.3541), correlated color temperature (CCT) of 6234 K, luminous efficacy of the radiation (LER) of 180 lm/W and 0.2345–0.2424 eV of activation energy for thermal quenching are obtained in the optimum phosphor YGO: 0.005Bi3+, 0.04 Tm3+, 0.07 Tb3+, 0.05Eu3+. The obtained results indicate that the YGO: Bi3+, Tm3+, Tb3+, Eu3+ phosphors can serve as potential color-tunable and single-phase white emission phosphors with impressive color stability as well as good thermal stability for n-UV excited white LEDs.