Novel red phosphors for light emitting diodes: Sr2-yCe1-xTixO4:YEu3+

A new luminescent inorganic oxide with the composition Sr2-yCe1-xTixO4:yEu3+ (0≤x≤0.03, 0.005≤y≤0.10), and as new near ultraviolet excited phosphors were synthesized using conventional solid-state reaction method and their luminescence properties under 365 nm excitation were investigated in detail. It indicated that, by doping small amount of Ti4+ into Ce4+ sites, the excitation intensity of charge transfer (CT) band of Ce4+-O2-(330-400 nm) was significantly broaden and enhanced. This can be explained by the special crystal structure of Sr2CeO4, which contained two kinds of Ce-O bonds: Ce-O-Ce and Ce-O-Sr, the incorporation of Ti4+ would change one of the Ce-O bond and result in the change of charge transfer band of Ce4+-O2-. As a result, the emission intensity of phosphor Sr2Ce1-xTixO4 have improved about 85% by doping 0.01 mol Ti4+. Sr2-yCe0.99Ti0.01O4:yEu3+ shows white emission at y≤0.01 because of the dominant intensities of 5D2 -7F0-3 transitions in blue-green region whereas the intensities of 5D0 -7F0-3 transitions in orange-red regions dominate at concentrations y≥0.03 and give red emission. Comparing with the commercial red phosphor Y2O2S:Eu3+, the Sr1.95Ce0.99Ti0.01O4:0.05Eu3+ phosphor exhibited excellent color purity and much higher brightness. The results showed that Sr1.95Ce0.99Ti0.01O4:0.05Eu3+ phosphors could be considered as a promising red phosphor for application in LEDs.

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