Sythesis And Properties Of Some Metal Ions Co-doped LnPO₄ Phosphors

With the development of nanotechnology,nanoscale luminescent materials have been widely used in various light-emitting devices because of their unique properties.The rare earth doped phosphates nano fluorescent materials exhibit excellent chemical stability,and high thermal stability.Meanwhile,those materials display interesting luminescent properties under ultraviolet and vacuum ultraviolet light excitation.Rare earth phosphates can be used as matrix of fluorescent materials and had been widely studied and applied.The development of new synthetic methods for preparation of rare earth phosphates with specific size,morphology,and excellent luminescent properties under mild conditions have important significance.The influence of the phase structure,grain size,morphology,and fluorescence properties of rare earth phosphates on the applications of phosphate phosphor should also be investigated.The rare earth ions and metals ions co-LnPO₄:RE³⁺,Mn⁺(Ln=Y,La;RE= Tb³⁺ Eu³⁺;Mn⁺= Mg²⁺,Ba²⁺,Ca²⁺,Sr²⁺,Cd²⁺,In³⁺,Mn²⁺)crystals were studied in this thesis.The X-ray diffraction（XRD）,scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FT-IR）,photoluminescence（PL）can be used the phase structure,size,morphology and fluorescence properties of the as-synthesized samples.The the effects of the synthesis conditions,the doping contents of alkaline earth metal ions or transition metal ion on the phase structure and optical properties of the rare earth phosphate materials were studied.Some new and interesting results were obtained and listed as follows.The alkaline earth metal ions co-doped YPO₄:1 at % Tb³⁺ fluorescent materials were synthetized via a hydrothermal process.The influence of the synthesis conditions such as reaction pH,hydrothermal temperature,hydrothermal reaction time and alkaline earth metal ions(Mg²⁺,Ba²⁺ doped and Mg²⁺,Ba²⁺ co-doped)on the phase structure and fluorescence properties of the products were investigated.Results show that the pH of reaction system,hydrothermal temperature,hydrothermal reaction time,and the doping contents of alkaline earth metal ions have an important effect on the phase structure and fluorescence properties.The results of XRD and FL show that the synthesized samples prepared at the pH is 6,the hydrothermal reaction temperature is 140 oC,and the hydrothermal reaction time is 24 h have better fluorescence performance than that obtained at other conditions.A series of pure phase Mg²⁺,Ba²⁺ and(Mg²⁺,Ba²⁺)co-doped YPO₄:1 at % Tb³⁺ phosphors with tetragonal xenotime structure（space group I41/amd）were synthesized by hydrothermal method.The phase structure and fluorescence properties of the samples were studied.The results show that a small amount of Mg²⁺,Ba²⁺ doped and(Mg²⁺,Ba²⁺)co-doped YPO₄:1 at % Tb³⁺ have less effect on the phase structure.When alkaline earth metal ions doping amount is higher than a certain amount,the as-prepared samples are compounds of the YPO₄ main phase mixed with a impurity phase.The pure phase with monoclinic monazite structure(Ca²⁺,Sr²⁺)doped/co-doped LaPO₄:1 at % Eu³⁺ fluorescent materials were successfully synthesized by a hydrothermal process.The influence of the synthesis conditions such as reaction pH,hydrothermal temperature,and doping content of alkaline earth metal ions on the phase structure and fluorescence properties were explored in this thesis.The results show that the samples synthesized under pH is 2,and the hydrothermal reaction temperature is 140 oC exhibit the pure phase and excellent luminescent properties.The Cd²⁺ and In³⁺ doped YPO₄:5 at % Tb³⁺ crystals,and Mn²⁺ doped YPO₄:5 at % Eu³⁺ fluorescent materials with different doping contents were prepared by a hydrothermal method.The influence of the doping contents of the transition metal ions on the phase structure and fluorescence properties of the samples were discussed.The XRD results show that a small amount of transition metal ions doped in the lattice of YPO₄:5 at % Tb³⁺ and YPO₄:5 at % Eu³⁺ have no obvious effect on the phase structure.Those as-synthesized samples are all pure phase YPO₄ crystals with tetragonal xenotime structure.However,the doping contents of the transition metal ions have substantial influence on the fluorescence properties of the samples.The excitation spectra and emission spectra results show that the samples posses the characteristic luminescence properties of the Tb³⁺ and Eu³⁺ ions.The relative intensities of the luminesncence spectra for those samples were increased with the doping contents of the doping ions increased,firstly,and then reached a maximum value and fell again.The as-prepeared samples display strongest relative intensities when the doping contents for Cd²⁺,In³⁺and Mn²⁺ are 1.5 at %,1.5 at %,and 0.5 at %,respectively.The mechanism of improved luminescence for those transition metal ions copoded samples were also discussed.