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

Abstract A series of novel Y 2 GeO 5 : Bi 3+ , Tm 3+ , Tb 3+ , Eu 3+ (YGO: Bi 3+ , Tm 3+ , Tb 3+ , Eu 3+ ) 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 Bi 3+ , Tm 3+ , Tb 3+ and Eu 3+ ions substitute for Y 3+ ions in host lattice of YGO without changing its crystal structure. Excitation and emission spectra were evaluated for the compounds. Energy transfer from Bi 3+ to Tm 3+ , Tb 3+ /Eu 3+ and Tb 3+ to Eu 3+ exist in phosphors YGO: Bi 3+ , Tm 3+ , Tb 3+ , Eu 3+ . Under the 308 nm excitation, the phosphor YGO: Bi 3+ , Tm 3+ , Tb 3+ shows the characteristic transitions of Bi 3+ (372 nm, 3 P 1 , 0  →  1 S 0 ), Tm 3+ (455 nm, 1 D 2 → 3 F 4 ), Tb 3+ (544 nm, 5 D 4 → 7 F 5 ). However, Eu 3+ 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 Bi 3+ to Tm 3+ 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: 0.005Bi 3+ , 0.04 Tm 3+ , 0.07 Tb 3+ , 0.05Eu 3+ . The obtained results indicate that the YGO: Bi 3+ , Tm 3+ , Tb 3+ , Eu 3+ 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.