Morphology And Photoluminescence Properties Of REPO₄ Nanocrystals Controled By Organic Phosphate

Based on the unique 4f energy level transition of rare earth elements,rare earth doped micro/nano materials have excellent optical,electrical and magnetic properties.Among them,REPO₄ has excellent physical and chemical properties,high chemical stability,and transparency in the near-ultraviolet and visible light regions.Recently,it has been used in light-emitting devices,biomarkers,molecular detection and optical imaging.It is well known that the luminescent properties of materials are highly sensitive to their phase composition,size and morphology.Recent researches focus on the structure and morphology of REPO₄ for enhancing the luminous properties of materials.In this paper,organic phosphoric acid was used as phosphorus source innovatively.The controlled structure synthesis of REPO₄ was achieved by solvothermal method combined with high-temperature calcination.The phase,size,morphology and photoluminescence properties of the prepared materials were characterized by powder X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,fourier transform infrared spectroscopy?FT-IR?,thermogravimetric-differential thermal synchronous thermal analysis?TG-DTA?,X-ray photoelectron spectroscopy?XPS?,photoluminescence spectrum?PL?and other characterization methods.The formation process and photoluminescence mechanism of different materials were discussed.The main contents of this paper are as follows:1.Coordination polymer submicrospheres were successfully synthesized by a solvothermal method using organophosphate?HDEHP?and Y?NO₃?₃ without any additional ligand and surfactant under mild conditions.Upon calcination of the obtained precursor,it produced stable tetragonal phase?t-?YPO₄ submicrospheres.XRD,SEM and HRTEM were used to characterize the precursor and calcined samples.The results showed that t-YPO₄submicrospheres were obtained by thermal decomposition of the precursor,and there was no other phase transition in the process.FTIR and TG-DTA confirmed that the precursor was coordination polymers formed by HDEHP and Y³⁺,and the growth process of the spherical precursor was proposed.Furthermore,various REPO₄?RE=La-Lu,except radioactive Pm?spherical particles and Eu³⁺doped YPO₄ phosphor were also synthesized under similar conditions.The luminescent properties of YPO₄:Eu phosphor were also studied in detail.2.With different organic phosphoric acids,P507,Cyanex272,phenylphosphonic acid,and phenylphosphinic acid as phosphorus sources,spherical,flower-like,nano-granular and massive YPO₄:Eu phosphors were obtained by solvothermal process combined with high-temperature calcination.The effects of solvothermal temperature and time,the molar ratio of organic phosphoric acid to rare earth ions and calcination temperature on the morphology of the product were studied in detail.By adjusting the above reaction parameters,the morphology control of YPO₄:Eu micro/nano crystals was preliminarily realized.PL spectra show that the obtained phosphors have strong red light emission,and the fluorescence intensities of YPO₄:Eu obtained from five system were compared.The results show that spherical YPO₄:Eu obtained from P507 system has the highest emission intensity.