Rare Earth Doped Bi_xO_yCl Layered Semiconductor Upconversion Luminescence And Near-infrared Photocatalytic Performance

The photodynamic therapy received extensive attention in the fields of treating tumors and cancer due to minimally invasive,non-toxic,and good targeting.However,the traditional photodynamic therapy mainly uses visible light as the excitation light source,resulting in poor penetration of treatment and limiting the therapeutic effect.In order to solve this problem,a combination of rare earth ion doped upconverting nanoparticles and a photocatalyst is proposed to form a composite photosensitizer,for example,NaYF₄:Tm³⁺/Yb³⁺nanoparticles and classical photocatalytic materials?such as TiO₂ or ZnO?.The principle is that the up-converting nanoparticle absorbs and converts the near-infrared light and then transmits it to the photocatalyst,which is essentially the indirect use of energy,and the energy transfer is impaired.Moreover,the photocatalyst is an important component of the composite photosensitizer,but the photocatalytic activity is limited because the photocatalytic excitation of the conventional photocatalyst is low.The Bi_xO_yCl quasi-two-dimensional layered semiconductor can induce the characteristics of the internal electric field due to the non-central symmetric layer structure,which can enhance the excitation efficiency of the carrier and prolong the carrier lifetime.Therefore,it can be combined with rare earth ions as an excellent up-conversion luminescent material,and it also has photocatalytic activity.It is a photocatalytic material that is expected to realize near-infrared self-conversion,and is characterized by direct self-conversion of near-infrared light and shows high utilization rate.It has been found that the luminescence and photocatalytic activity of Bi_xO_yCl quasi-two-dimensional layered semiconductors are dependent on the spontaneous internal electric field,while the internal electric field depends on the size and thickness of the vertical scale.The size reduction of the material can effectively enhance the internal electric field and enhance the photoelectric conversion efficiency,which enhance luminescence intensity and photocatalytic activity.And after thinning,the smaller size can enter the biological tissue,combining with its near-infrared photocatalytic properties,it is hopeful to achieve photodynamic therapy in the living body.Based on the above mentioned,two schemes of chemical thinning and mechanical thinning were designed for the different structures of BiOCl and Bi₃O₄Cl,and the internal electric field of Bi_xO_yCl layered material was enhanced by thinning the thickness.But in fact,the size reduction of the layered material has two effects:on the one hand,it has been found that a large number of defects are generated on the surface of the material when the size of the Bi_xO_yCl layered material is reduced to a size of a few nanometers,which will lead to a quenching effect of upconversion luminescence;on the other hand,the size reduction significantly enhances the internal electric field of the Bi_xO_yCl layered material,enhances the excitation efficiency of the photogenerated carriers and the lifetime of the intermediate level of the rare earth ions,thus the influence for upconversion luminescence is a synergistic effect.However,we found that the synergistic effect of the internal electric field on the upconversion luminescence of rare earth ions in the Bi_xO_yCl system is dominant when the material size is thinned,and depending on the surface defects.the sample has a photocurrent response under 980 nm near-infrared laser excitation,which is also the basis for the material to exhibit near-infrared photocatalytic activity.Therefore,when the size of the Bi_xO_yCl layered material is thinned,the up-conversion luminescence of the rare earth ions and the near-infrared photocatalytic activity of the material are simultaneously enhanced.