Novel color tunable phosphors NaYGeO 4 : Tm 3+ , Tb 3+ , Eu 3+ for ultraviolet excited white LEDs with good thermal stability

Single-phased phosphors NaYGeO4: Eu3+, Tb3+, Tm3+ were synthesized by a high temperature solid-state reaction. Upon the excitation of 300–325 nm, the NaYGeO4: Eu3+, Tb3+, Tm3+ phosphors emit combining blue, green and red lights, coming from the characteristic emissions of Tm3+, Tb3+, Eu3+, respectively. Mechanisms of concentration quenching and energy transfer from Tb3+ to Eu3+ have been investigated. The emission color can be adjusted by tuning the doping contents appropriately. The optimal NaYGeO4: 0.12Eu3+, 0.07Tb3+, 0.03Tm3+ phosphor emits a warm white light with chromaticity coordinate of (0.3521, 0.3761), correlated color temperature of 4842 K, activation energy for thermal quenching effect of 0.213–0.225 eV and internal quantum efficiency of 40.2%. The obtained properties indicate that NaYGeO4: Eu3+, Tb3+, Tm3+ phosphor might be a promising single-phased white light emitting phosphor for UV-pumped white-LED.