Investigation Of High-efficiency UVC Upconversion Materials With Sunlight-activated

UVC upconversion luminescent materials have potential applications in sewage treatment,information storage,3D printing and other fields.UVC upconversion,under the excitation of non-laser sources especially under the sunlight,is more suitable for large area sewage treatment and self-cleaning of buliding surfaces.And since the short ultraviolet part of sunlight is absorbed by the Earth’s ozone layer,there is no short ultraviolet natural light on the surface of the Earth,thus the biological phototaxis can be utilized to apply to environmental protection.In this paper,we mainly studied the spectral properties,energy transfer mechanism and the conditions of UVC upconversion luminescence by a series of oxides and fluorides doped with Pr³⁺ions under the excitation of blue laser and sunlight.The UVC emission power and conversion efficiency of the UV upconvertion material were calculated,and the efficient UVC upconversion material YBO₃:Pr³⁺was successfully applied to the biological sterilization experiment.The main contents and results are as follows:（1）1mol%Pr³⁺doped YBO₃,LuBO₃,LaBO₃,YPO₄,LuPO₄,LaPO₄,LiYF₄,NaYF₄,Cs₂NaYF₆ and Y₂SiO₅ were synthesized by high temperature solid state reaction.The XRD proved that the synthesis of this series of materials is pure phase.We have researched the mechanism of UVC emission from the 4f5d level of Pr³⁺ion excited by blue light and X-ray,and obtained the condition to generate UVC UC emission,namely,the lowest 5d band of the4f5d states must be below the conduction band of a host as well as the ¹S₀ level in a Pr³⁺doped phosphor.（2）The UV photon images of the fluorescent material under sunlight and 450 nm LED laser excitation were obtained.The UVC upconversion efficiency and emission power of the material under sunlight and 450 nm laser were calculated by UV imager calibration.Through the logarithm relationship between excitation density and the UVC emission,the data proved that the UVC upconversion emission of the material under the excitation of sunlight and laser is a two-photon process and comes from the same mechanism.In this paper,the most efficient UVC upconversion material YBO₃:Pr³⁺was obtained,which can reach up to 8 mW/cm²under 450 nm laser and 0.1 mW/cm² under sunlight excitation,respectively,and about 3 times higher than that of Y₂SiO₅:Pr³⁺,Li⁺explored by Cates’group.（3）The efficient UVC upconversion material YBO₃:Pr³⁺was applied to the biological sterilization experiment under sunlight excitation.