| Recently,Pr3+ doped CaTiO3 red emitting powders have been widely investigated due to their high chemical stability,strong and sharp red emission,and high brightness.Moreover,Pr3 doped MTiO3 materials have shown a great potential in the fields of emission displays(FEDs),plasma display panels(PDPs),and ultraviolet light-emitting diodes(UV-LEDs).Royce et al.first demonstrated that the luminescent intensity and long afterglow were significantly elevated by substituting Zn2+ for Ca2+.After that,many researchers have been focused on their structures and properties,especially luminescence properties.As previously reported the nominal composition as Ca0.8Zn0.2TiO3:0.05%Pr3+ phosphor is a kind of high color purity and high brightness of red phosphors which can be effectively stimulate by located at 380 nm broadband wavelength,indicating that Ca0.8Zn0.2TiO3:0.05%Pr3+ is a potential red phosphor for the near-UV-pumped white LED.However,the emission intensity is not strong enough for practical application.So how to improve the red luminous intensity of Ca0.8Zn0.2TiO3:Pr3+ phosphor is a problem to be solved.In this paper,a series of phosphors with nominal composition of Ca0.8Zn0.2Ti03:0.05%Pr3+ were 'synthesized by an ethylene glycol assisted hydrothermal method.The effects of Zn2+ concentration,ethylene glycol amount,adding occasion,hydrothermal temperature,hydrothermal time and pH value of the precursor solution on photoluminescence and phase composition were studied.Meanwhile,pure CaTiO3:Pr3+Zn2TiO4:Pr3+and Ca2Zn4Ti16O38:Pr3+ powders were obtained by the similar process.The phosphors were characterized by powder X-ray diffractioner(XRD),UV-vis spectrophotometer and luminescence spectrofluorometer.Moreover,the relationship of phase contents and luminescence properties of Ca0.8Zn0.2TiO3:0.05%Pr3+ phosphors have been discussed through quantitative phase analysis(WPF Refinement)method.The photoluminescence of nominal composition as Ca0.8Zn0.2TiO3:0.05%Pr3+ phosphors with distinct phases were compared with the pure CaTiO3:Pr3+,Zn2TiO4:Pr3+ and Ca2Zn4Ti16O38:Pr3+ powders.The specific contents are as follows:1.Compared with the luminescence properties of samples were synthesized by high temperature solid phase method,sol-gel method,hydrothermal method and ethylene glycol assisted hydrothermal method,respectively.The results showed that the luminescence intensity of phosphors by four methods have the following pattern:high temperature solid phase method<sol gel method<hydrothermal method<ethylene glycol assisted hydrothermal method.2.A series of phosphors with nominal composition of Ca0.8Zn0.2TiO3:0.05%Pr3+ were synthesized by an ethylene glycol assisted hydrothermal method,such as:(1)Phosphors consist of CaTiO3,Ca2Zn4Ti16O38 and Zn2TiO4 three phases,i.e.sample SS-32-235-6.8;(2)Phosphors consist of CaTiO3 and Zn2TiO4 two phases,i.e.sample SS-32-280;(3)Phosphors consist of CaTiO3 and Ca2Zn4Ti16O38 two phases,i.e.sample SL-40.The results show that the sample SS-32-235-6.8 has the strongest luminescence properties,which are 1.3 and 2.7 times than that of sample SL-40 and sample SS-32-280 under excited by 330 nm wavelength,respectively.Excited by 380 nm wavelength are 1.8 and 3.6 times,respectively.The optimized pH value at pH=6.8 and pH=5.9,respectively.The chromaticity coordinates was located at(x=0.667,y=0.332).The photograph of sample prepared at pH=5.9,which excited by a 365 nm NUV lamp show a wonderful red emission.Results suggest that Ca0.8Zn0.2TiO3:Pr3+is a potential red phosphor for near-UV-pumped white LEDs.3.Pure CaTiO3:Pr3 phosphor powder is obtained by an ethylene glycol assisted hydrothermal method.The effects of pH value of the precursor solution on photoluminescence and phase composition were studied.Results suggest that the single-phase CaTiO3:Pr3+ phosphor can be obtained only in nearly neutral or weak alkaline conditions(7<pH<9),however,the TiO2 impurity will be yielded in weak acidic(pH = 6.1,)or weak alkaline(pH = 10.8,e.g.)conditions.4.Pure Ca2Zn4Tii6O38:Pr3+phosphor powder is obtained by an ethylene glycol assisted hydrothermal method.The luminescence properties of phosphor were optimized.Results show that the single-phase Ca2Zn4Ti16O38:Pr3+ phosphor can be synthesized when the mole ratio of nCa:nZn:nTi is equal to 1:2.05:7.5.Similarly,as molar ratio of nCa:nZn:nTi is 1:2.1:7.5,the CZT16O powders with a trace ZTO can be obtained.5.Pure Zn2TiO4:Pr3+ phosphor is synthesized by an ethylene glycol assisted hydrothermal method,when the mole ratio of n(Zn):n(Ti)=2:1,pH=6.0,and the calcination temperature is between 700 and 1100?.However,the luminescence is weak. |
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