Synthesis And Luminescence Of Rare Earth Ions Doped Titanate Phosphors

As a solid state lighting source, white light emitting diodes (WLEDs), which are known as the forth-generation lighting source, have many advantages such as long serving longevity, energy saving, environmental amity, requirement of low voltage support and fast response, etc. and have received extensive attention. Generally, there are two major routes to achieve WLED:one is by assembling red, green and blue LED chips to achieve white light emission; another is by combining blue or ultraviolet LED chip with rare earth doped phosphors to achieve white light emission. The progress in preparation technology of phosphors greatly drives the development of WLED. In this dissertation, the rare earth ions doped titanate materials for UV chip-based WLEDs were investigated.Trivalent rare earth ions (RE3+) possess many levels, and RE3+ doped luminescent materials have broad application prospects in the lighting, biological fluorescence labling, short wavelength lasers, information displays and optoelectronics. Titanates have good thermal and chemical stability and are excellent matrics for RE3+ luminescence centers. In this dissertation, rare earth doped titanate luminescent materials were successfully synthesized through traditional high temperature solid-state method. The synthesis conditions, luminescence properties and thermal stability of the titanate phosphors were analyzed by means of x-ray diffraction (XRD), fluorescence spectroscopy, and chromatric calculations. The main contents and results are as follows.The Eu3+ doped NaGdTiO4 red phosphors were synthesized through high temperature solid-state method. The optimal preparation condition of NaGdTiO4:Eu3+ phosphors was studied, and that the optimized ratio of raw materials was determined. The results showed that there is a strong energy transfer from the matrix to the Eu3+ ions; the samples can be effectively excited by UV light and have intense red light emission. The analysis of fluorescence decay curves at different temperatures confirmed that energy transfer from Eu3+ to quenching center is the major mechanism of fluorescence thermal quenching of Eu3+ ions in NaGdTiO4 phosphors.The Dy3+ doped NaGdTiO4 white light phosphors were synthesized through high temperature solid-state method. The influences of the raw materials, flux content and the activator concentration on the properties of the phosphors were studied in detail. It was found that the doping concentration of Dy3+ ions does not affect the crystal structure of the samples and there is an effective energy transfer from the matrix to the Dy3+ ions; the high quality white light emission can be achieved from the studied phosphors. With the increase of temperature the thermal quenching phenomenon happened. Analysis on the temperature-dependent fluorescence decay curves and the emission intensity indicated that the cross-over process is the major mechanism of fluorescence thermal quenching of Dy3+ ions in NaGdTiO4 phosphors.The Er3+/Yb3+ co-doped NaGdTiO4 upconversion phosphors were synthesized through high temperature solid-state reaction method. It was found that the two-photon process is responsible for both green and red upconversion emissions of Er3+ in NaGdTiO4:Er3+/Yb3+ phosphors. The relationship between Er3+ doping concentration and upconversion luminescence intensity was studied. Finally, the specific process of upconversion luminescence of NaGdTiO4:Er3+/Yb3+ phosphor was discussed.