Controlling the Energy Transfer via Multi Luminescent Centers to Achieve White Light/Tunable Emissions in a Single-Phased X2-Type Y2SiO5:Eu3+,Bi3+ Phosphor For Ultraviolet Converted LEDs

So far, more than 1000 UV converted phosphors have been reported for potential application in white light-emitting diodes (WLEDs), but most of them (e.g., Y2O2S:Eu, YAG:Ce or CaAlSiN3:Eu) suffer from intrinsic problems such as thermal instability, color aging or re-absorption by commixed phosphors in the coating of the devices. In this case, it becomes significant to search a single-phased phosphor, which can efficiently convert UV light to white lights. Herein, we report a promising candidate of a white light emitting X2-type Y2SiO5:Eu3+,Bi3+ phosphor, which can be excitable by UV light and address the problems mentioned above. Single Bi3+-doped X2-type Y2SiO5 exhibits three discernible emission peaks at similar to 355, similar to 408, and similar to 504 nm, respectively, upon UV excitation due to three types of bismuth emission centers, and their relative intensity depends tightly on the incident excitation wavelength. In this regard, proper selection of excitation wavelength can lead to tunable emissions of Y2SiO5:Bi3+ between blue and green, which is partially due to the energy transfer among the Bi centers. As a red emission center Eu3+ is codoped into Y2SiO5:Bi3+, energy transfer has been confirmed happening from Bi3+ to Eu3+ via an electric dipoledipole (dd) interaction. Our experiments reveal that it is easily realizable to create the white or tunable emissions by adjusting the Eu3+ content and the excitation schemes. Moreover, a single-phased white light emission phosphor, X-2-type Y1.998SiO5:0.01Eu3+,0.01 Bi3+, has been achieved with excellent resistance against thermal quenching and a QE of 78%. At 200 degrees C, it preserves >90% emission intensity of that at 25 degrees C. Consequent three time yoyo experiments of heating-cooling prove no occurrence of thermal degradation. A WLED lamp has been successfully fabricated with a CIE chromaticity coordinate (0.3702, 0.2933), color temperature 4756 K, and color rendering index of 65 by applying the phosphor onto a UV LED chip.