Photoluminescence and tunable emissions of La2(GeO4)O:Bi3+, Eu3+ phosphor for ultraviolet converted light emitting diodes

In the past decades, a great variety of single-phase white-emitting phosphors have been developed, however most them can't satisfy us due to their low quantum efficiency and poor thermal stability. Herein, we reported a promising candidate of a white-emitting La2(GeO4)O:Bi3+/Eu3+ phosphor, exhibiting an efficient energy transfer, good thermal stability and high quantum efficiency. Rietveld structure refinement of La2(GeO4)O:Bi3+ was performed to confirm Bi3+ occupation of La sites in La2(GeO4)O. An analysis on the red-shift of both excitation and emission spectra of La2(GeO4)O:Bi3+ was made by combining the crystal structure and their spectroscopy. Thermal quenching temperature (T50%) of La2(GeO4)O:Bi3+ was approximately 532 K which is higher than that (473 K) of the LED chips under high power current driving and La2(GeO4)O:Bi3+ presented a spectral blue-shift as an increase in temperature. Furthermore, thermal quenching of La2(GeO4)O:Bi3+ was explained in detail by the configurational coordinate. More importantly, single Bi3+ doped La2(GeO4)O presented a blue-greenish broad band at 480 nm with a high quantum efficiency (48%) and excellent thermal stability (ΔE = 0.353 eV). Energy transfer from Bi3+ to Eu3+ in La2(GeO4)O efficiently occurred and energy transfer mechanism of Bi3+→Eu3+ was demonstrated to be dipole-quadrupole interaction. By codoping Eu3+ in La2(GeO4)O:Bi3+, La2(GeO4)O:Bi3+, Eu3+ phosphor exhibited the blue-green and red dual emissions. Fortunately, a single-phase white-emitting phosphor La1.94(GeO4)O:0.03Bi3+, 0.03Eu3+ was obtained with excellent resistance against thermal quenching and a quantum efficiency of 37%.