Preparation And Luminescence Properties Of Blue-emitting Na_xK_1-xSrPO₄:Re (Re=Eu²⁺, Tb³⁺) Phosphors

White light emitting diodes (WLEDs), fabricated with near-ultraviolet (NUV) LED chips and RGB tri-color phosphors, have many important applications in illumination and display area. This thesis focuses on the high-temperature solid-state synthesis, structural characterization, and luminescence properties of a kind of Na_xK_1-xSrPO₄:Re (Re=Eu²⁺, Tb³⁺) blue-emitting phosphors, which can be efficiently excited with NUV chips and has potential applications in high color-rendering WLEDs. Emphasis is placed on the elucidation of the effect of Na⁺ concentration on the structural and luminescent properties (both brightness and color) of Na_xK_1-xSrPO₄: Eu²⁺ phosphors. Moreover, the effect of Tb³⁺ co-activator on phosphor photoluminescence properties is also investigated.The result of photoluminescence characterization showed that Na_xK_1-xSrPO₄:Eu²⁺ could be the effectively excited by NUV excitation, and displayed two bands centering at 435 nm and 490 nm, respectively. With increase in Na⁺ concentration, intensity of the band at 435 nm was gradually reduced, while that at 490 nm was enhanced. As a result, the emission color of Na_xK_1-xSrPO₄:Eu²⁺ was shifted from deep blue to cyan gradually with increase of Na⁺ ion and finally turned white when all K⁺ ions were substituted with Na⁺. Cathodoluminescence of Na_xK_1-xSrPO₄:Eu²⁺ also showed that the intensity of the peak around 490nm enhanced with the doping concentration of the Na⁺ ions increasing, and all the phosphor granules were brightened up uniformly under electron bombarding. The results above suggest that Na⁺ ions uniformly substituted K⁺ ions in the host of KSrPO4. The emission peaks generated redshift because the smaller radius of Na⁺ ion enhanced the crystal field splitting of 5d energy level of Eu²⁺ ions. After the doping of the second activator Tb³⁺ ions, the emission peaks which corresponding to 5D4â†'7F6,5D4â†'7F5,5D4â†'7F4 and 5D4â†'7F3 of the Tb³⁺ ions were observed in the luminescence spectra of Na_0.6K_0.4SrPO₄: Eu²⁺, Tb³⁺. With the increase of Tb³⁺ concentration, the intensity of Tb³⁺ emission was enhanced, and the intensity of Eu²⁺ emission was lowered down. The emission spectra and the excitation spectra proved the existence of energy transfer from Eu²⁺ to Tb³⁺. In summary, Na_xK_1-xSrPO₄:Re (Re=Eu²⁺, Tb³⁺) is a promising WLED blue-emitting phosphors, besides its excellent cathodoluminescence property suggests that it has promising applications in cathodoluminescence devices.