α-Sr2SiO4:Ce3+, Dy3+, Na+ phosphors with abnormal thermal quenching properties for solid-state lighting applications

There is urgent need of thermally stable phosphors for fabricating high-performance white light emitting diodes (LEDs). In this paper, Sr₂SiO₄:0.02Ce³⁺,xDy³⁺, (0.02+x)Na⁺ phosphors were successfully synthesized by the solid-state reaction method and their luminescence properties were studied. Phase analysis shows that single-phasic α-Sr₂SiO₄ was prepared when x was greater than 0.006, while a mixed phase of α-Sr₂SiO₄ and β-Sr₂SiO₄ were obtained in the samples with x of 0.006 or less. When excited at 344 nm, there is a major emission band at 380–500 nm corresponding to the 5d-4f transition of Ce³⁺, and other emission peaks with a dominated one at 575 nm corresponding to the ⁴F_9/2-⁶H_13/2 transition of Dy³⁺. The as-developed Sr₂SiO₄:Ce³⁺,Dy³⁺,Na⁺ phosphors exhibit excellent thermal stability. To be specific, the intensity retention rate of 425 and 572 nm at 300 °C is as high as 103.6 % and 89.2 %, respectively. Furthermore, near-ultraviolet (nUV) chip-pumped white LED prototypes were assembled using the co-activated phosphor and commercial green and red phosphors, which demonstrate its great potential in high-power white LEDs for solid-state lighting applications.