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Preparation and Luminescence Properties of Blue-emitting NaxK1-xSrPO4:Re (Re=Eu2+, Tb3+) Phosphors

Author: BianZuoZuo
Tutor: ZhangZuoTong
School: Northeast Normal University
Course: Condensed Matter Physics
Keywords: White LEDs (WLEDs) Blue-emitting phosphors Phosphate Eu2+ activator Energy transfer Cathodoluminescence
CLC: O482.31
Type: Master's thesis
Year: 2011
Downloads: 50
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Abstract


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 NaxK1-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 NaxK1-xSrPO4: Eu2+ phosphors. Moreover, the effect of Tb3+ co-activator on phosphor photoluminescence properties is also investigated.The result of photoluminescence characterization showed that NaxK1-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 NaxK1-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 NaxK1-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 5D4→7F6、5D4→7F5、5D4→7F4 and 5D4→7F3 of the Tb3+ ions were observed in the luminescence spectra of Na0.6K0.4SrPO4: 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, NaxK1-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.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Solid nature of the > Optical Properties > Luminescence
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