Preparation And Applications Of UVC Upconversion Luminescence Materialsunder The Low Excitation Density

Upconversion material has potential application in biomedicine, information storage, solar cells and so on. Especially the short ultraviolet rays UVC, it is of great value in the areas of biomedicine.But almost allof the reported upconversion luminescence emissions can only be achieved under the laser excitation, whichgreatly restricts its practicability.In this paper, the UVC emissions are obtained through Y₂SiO₅:Pr³⁺,Li⁺, LiYF₄: Pr³⁺and Y?PO₃?₃: Pr³⁺ phosphors under sunlight excitation. The spectralproperty and energy transfer mechanismare analyzed, and the materials wereapplied in photocatalysis and microbial inactivation. The main contents and result as following:?1? The spherical mesoporous silica?MCM-48?, which average particle size was about 400 nm and the mesoporous channels calculated value of diameter was about 3.31 nm, was successfully synthesized byhomogeneous precipitation method. Then the various concentrations of Y₂SiO₅:Pr³⁺,Li⁺microcrystalswere synthesizedviaa hydrothermal method. The X-ray powder diffraction?XRD? andemission spectra were used to characterizeY2 Si O5:Pr³⁺,Li⁺microcrystals with different Pr³⁺ and Li⁺concentration, and it concluded thatthe best concentration of Pr³⁺ and Li⁺was 1.2% and 9%, and the best calcinedtemperature was 1100?.The emission spectrawere proved that UV upconversion emission ofY₂SiO₅:Pr³⁺,Li⁺can be efficiently transferred to TiO₂.So Y₂SiO₅:Pr³⁺,Li⁺/TiO₂ composites can be efficiently used in photocatalysis.And the degradation rate of Y₂SiO₅:Pr³⁺,Li⁺/TiO₂ composites was about 14 timesas high as that for pure TiO₂ under xenon lamp.?2? LiYF₄: Pr³⁺was synthesized by the high temperature solid-state method. The X-ray powder diffraction was proved that the pure phase LiYF₄ was obtained. The UV images of LiYF₄: Pr³⁺microcrystal under sunlight excitation was observed with theUV imager.And the UVC UC emissions of LiYF₄: Pr³⁺excited by a 488 nm laser and sunlight were compared.It indicated that UVC upconversion emission can be observed in a LiYF₄: Pr³⁺microcrystal under sunlight excitation.The two-photon processes play an important rolein UVC UC emission was proved through the logarithm relationshipbetween excitation density and the emissionintensity. The UVC UC mechanismsunder the excitation of a488 nm laser and sunlight were presentedand discussed. The ET and ESAprocesses were pivotal in the population of high-energy levelsunder sunlight excitation.?3? Y?PO₃?₃: Pr³⁺, Li⁺phosphors were synthesized by the high temperature solid-state method. The phase and structure have been investigated by the X-ray powder diffraction,indicating that pure phase Y?PO₃?₃was obtained. By comparing the excitation and emission spectra of Y?PO₃?₃: Pr³⁺,LiYF₄:Pr³⁺andY₂SiO₅: Pr³⁺, Li⁺, we know thatthe emission energy of Y?PO₃?₃: Pr³⁺ wasfocused on UVC, and Y?PO₃?₃: Pr³⁺more suitable for application in biological sterilization. By discussingthe band gap of Y?PO₃?₃,LiYF₄ and Y₂SiO₅, we explained 4f5 d of Pr³⁺ in Y?PO₃?₃ from 3PJ more further. Raman spectra illustrated the maximum phonon energy of Y?PO₃?₃was 1203 cm-1, and the P-O-P bond length of the material was 0.1638 nm.UV images of Y?PO₃?₃: Pr³⁺, Li⁺under sunlight excitation were also obtained.UVC upconversion emission undersunlight excitationin the material Y?PO₃?₃: Pr³⁺, Li⁺ was observed, and it resultedin significant microbial inactivation.