Research On Upconversion Luminescence And Regulation Behavior Of Yb³⁺-Eu³⁺ Doped BiOCl Layered Semiconductors

BiOCl is a kind of two-dimensional layered material with oriented spontaneous internal electric field.Under the action of spontaneous internal electric field,photogenerated electron hole separation can also be directionally separated,which shows unique ferroelectric photovoltaic effect.Rare earth ion Eu³⁺is a kind of luminescent ion which is highly sensitive to the external environment.In this paper,the up-conversion system of BiOCl doped with Eu³⁺-Yb³⁺was studied.From the doping matrix component of sensitizer Yb ion,the radial scale of BiOCl layered matrix,and the doping of isoradius heterovenous Ca²⁺ion,the electrodipole transition behavior of Eu³⁺ion was used as a probe to explore the regulation behavior of this new up-conversion luminescence system.The main results are as follows:Under 980 nm laser irradiation,Eu³⁺ions exhibit a significant ⁵D₀?⁷D₄?698 nm?far red emission in the solid-state synthesis of BiOCl microsheet crystals.The transition fraction ratio of ⁵D₀?⁷F₂?614 nm?and ⁵D₀?⁷D₄?698 nm?of Eu³⁺ions and the splitting behavior of Starks level increase with the increase of laser luminosity.However,with the increase of sensitizer Yb ion concentration,the transition ratios of ⁵D₀?⁷F₂?614 nm?and ⁵D₀?⁷D₄?698 nm?of Eu³⁺ion and the splitting behavior of Starks level decrease.Its composition and power regulation show contradictory behavior with traditional upconversion materials.It is found that under the action of 980 nm laser,the layered BiOCl system not only produces intensely oriented photoinduced polarization field,but also forms a new anti-Stokes ferroelectric photovoltaic effect under the interaction of Yb ions.That is to say,the combination of these layered substrates with spontaneous internal electric field and rare earth upconversion produces a new regulatory mechanism.In the hydrothermal synthesis of BiOCl nanosheet crystal system,we achieved the control of the post-nanosheet by reaction time.It is found that besides depending on the power of the incident laser,the electric dipole transitions of Eu³⁺ions ⁵D₀?⁷F₂?614 nm?and ⁵D₀?⁷D₄?698 nm?can be effectively controlled by the thickness of the lamella.Contrast experiments show that besides the anti-Stokes ferroelectric photovoltaic effect,with the decrease of the radial scale of nano-sheet crystals,the photoinduced polarization field of orientation increases greatly under 980 nm laser irradiation.The upconversion regulation of these layered matrices is strongly scale dependent.This discovery is helpful for us to understand the photophysical properties of two-dimensional layered materials in nano-scale,and provides ideas for the development of new nano-optoelectronic devices.BiOCl microcrystals doped with Ca²⁺-Yb³⁺-Eu³⁺were prepared by solid-state method.It is found that the spontaneous internal electric field and ferroelectric photovoltaic effect of layered BiOCl can be strongly changed by Ca²⁺ion substituting Bi³⁺with different valence through Eu³⁺down-conversion probe.The results show that the down-conversion luminescence of Ca²⁺doped BiOCl:1%Eu³⁺,5%Yb³⁺samples shows a highly sensitive wavelength dependence.By comparing the samples of Ca²⁺doped BiOCl:1%Eu³⁺microcrystals,it is found that Yb³⁺doping will affect the way Ca²⁺ions enter BiOCl lattice,thus affecting the down-conversion luminescence and fluorescence lifetime of Eu³⁺ions.The upconversion luminescence of Eu³⁺can be controlled by Ca²⁺doping concentration and laser power.