Synthesis And Properties Of Rare Earth Doped BiPO₄ Materials

At present,the global economy has entered an era of rapid development,and environmental pollution and energy crisis are particularly prominent.Compared with traditional lighting sources such as high-pressure gas discharge lamps,fluorescent lamps,and incandescent lamps,the white LED as the fourth generation light source has significant advantages in terms of energy saving,environmental protection,efficiency,response speed,and service life.The blue chip plus Y₃Al_l5O₁₂:Ce³⁺yellow phosphor has become the main process for producing white LEDs at present.However,There is almost no red light component,making the color rendering index?CRI?low,so the key is to explore and research new types of red phosphors.Phosphate has good physicochemical stability.Bi PO₄ is similar to lanthanide orthophosphate,the valence of Bi³⁺ion is like with trivalent rare earth ion,and the ionic radius is similar.It has become an excellent luminescent material matrix.In this dissertation,hydrothermal synthesis method was used to prepare phosphors with pure low-temperature monoclinic phase and excellent luminescence properties by using BiPO₄ as the host material.Through a single doping and double doping of rare earth ions,and introduction of alkali metal ions,a dimmable red phosphor is realized.The reasons for the increase in luminous intensity and the factors that led to changes in its structure and morphology were discussed.The main results are as follows:?1?The hydrothermal method was used to synthesize BiPO₄:Eu³⁺red phosphor at the reaction temperature of 180°C and pH=1.0.When the reaction time was 12 h,the crystallinity was the highest and the luminescent property was the best.The BiPO₄:Eu³⁺red phosphors synthesized under different Eu³⁺doping amounts belong to the low temperature monoclinic phase.When the doping amount of Eu³⁺is 7%,the luminescence intensity reaches a maximum value.?2?The EDTA-Na₂ assisted hydrothermal method was used to synthesize BiPO₄:Eu³⁺red phosphor under the conditions of reaction temperature of 180°C,reaction time of 12 h,and pH of 0.5,to study the performance of different morphological samples.Luminescence properties were best when the amount of EDTA-Na₂ added was 4 mmol.When Na₃PO₄·12H₂O was used as the phosphorus source,the SEM data showed that when the pH was set to 1.2,the crystals became uniform burrballs.As the pH value increased,the microrods became thinner.When NH₄H₂PO₄ was used as the phosphorus source,a small amount of hexagonal phase began to appear as the pH value gradually increased.pH value had little effect on the morphology of the crystal,and the luminescence intensity was the strongest at pH=0.5.?3?BiPO₄:Eu³⁺,Dy³⁺phosphors were synthesized by hydrothermal method under the conditions of reaction temperature 180°C,reaction time 12 h,pH=1.0,single host Bi PO₄:Dy³⁺emitting white light was realized.BiPO₄:Eu³⁺,Dy³⁺phosphors with different doping concentrations of Dy³⁺are low-temperature monoclinic phase,and the luminescence intensity increases first and then decreases gradually with increasing doping concentration of Dy³⁺.The CIE chromaticity coordinate point moves from the red orange light to the white light position.It can be seen that a wide range of dimming of BiPO₄:Eu³⁺,Dy³⁺phosphors can be achieved by adjusting the doping concentration of Dy³⁺,and this phosphor can be used in lighting.?4?The hydrothermal method was used to prepare BiPO₄:Tb³⁺,Eu³⁺phosphors under the conditions of reaction temperature 180°C,reaction time 12 h,pH=1.0.The sample structure changed with the increase of Eu³⁺ion concentration,and the morphology was composed of rods.There is energy transfer between Tb³⁺and Eu³⁺,and the form of energy transfer can be determined by calculation.From the CIE chromaticity coordinate diagram,the color of the fluorescent light emitted from the yellow,orange yellow to the red region was sequentially shifted,indicating that the light adjustment can be achieved by adjusting the doping ratio of Tb³⁺and Eu³⁺.?5?BiPO₄:Sm³⁺,A?Li⁺,Na⁺,K⁺?orange-red phosphors were synthesized by hydrothermal method under the conditions of reaction temperature 180°C,pH=1.0.All the samples were in low temperature monoclinic phase.The crystallinity of three alkali metal ions A?Li⁺,Na⁺,K⁺?and Sm³⁺co-doped BiPO₄ based phosphors is higher than that of single doped Sm³⁺,and the XRD diffraction peaks of the doped samples are slightly shifted.It can be seen from the emission spectrum that co-doped alkali metal ions the luminescence intensity of the samples is higher than that of the single doping of Sm³⁺ions,and the order of the luminous intensity enhancement effect is:Li⁺>K⁺>Na⁺.