Luminescence And Temperature Detection Behavior Of Rare Earth Ions Under The Evolution Of Layered Structure Of Bismuth Oxyfluoride Semiconductor

Because the in-plane covalent bonding of strongly electronegative atoms is connected by the van der Waals force between layers,the direction and process of electron movement in the layered matrix is limited by the anisotropy of the crystal structure which will produce unique physical,electronic,chemical and photoelectric properties.Combined with rare ions,layered materials may change the luminescence behavior of rare earth ions resulting in an unique luminescence phenomenon compared with traditional three-dimensional structure materials,and achieve the development of its performance and application fields.Bismuth oxyfluoride（BiOF）is a typical layered direct band gap semiconductor material.Due to the existence of the strong electric dipole moment of the F^-ions,structural evolution of BiOF may transform the material transition and build-up to have a more serious impact compared with other bismuth-based layered crystals,which contributes to understanding the rule of the layered structure on the emission of rare earth ions.In this paper,we selected BiOF and Bi₇F₁₁O₅ with similar components and different layered structures of bismuth oxyfluoride semiconductors,and studied their effects on the rare earth ion Eu³⁺and the luminescence behavior of Er³⁺.The results show that the Bi₇F₁₁O₅ has stronger mutation properties and high carrier separation effect induced by the strong dipole moment group and layered structure,compared with BiOF,which has simpler structure and high symmetry.This characteristic has changed the transition rule and luminescence properties of rare earth ions at high temperature,and we have explored the application of rare earth ions doped Bi₇F₁₁O₅ system in fluorescent temperature sensing.The main findings are as follows:For BiOF with a simple sandwich structure,we improved the synthesis method.A solvothermal method was used to synthesize the BiOF nano single crystal with scale,controllable thickness and better dispersion for the first time.This synthesis method solved the problems that easy to produce agglomeration and weak orientation growth due to the the electronegativity of F^-ions in the previous study.The luminescence behavior of Er³⁺,Eu³⁺ions indicated BiOF crystal has a strong depolarization effect and a orresponding strong built-in electric field duo to the strong dipole moment,compared with the same structure and size of the bismuth oxyhalide crystals.However,due to the anti-scale enhancement effect of the back-bias effect,the excitation field enhancement of the built-in electric field and the separation of electron interactions,the luminescence intensity and fluorescence lifetime of rare earth ions decrease with the scale of BiOF crystal rises.This discovery brings new ideas to the design and develop of new nano-luminescence and optoelectronic materials.We synthesized orthorhombic bismuth oxyfluoride Bi₇F₁₁O₅ by solvothermal and solid state reaction in two steps.Combining the theoretical calculations and experiments,we found that Bi₇F₁₁O₅ has a stronger polarizabilty and a strong IEF due to the larger dipole moments produced by Bi³⁺ion has four different lattice positions,the stronger polarizabilty promotes Eu³⁺to achieve far-red light emission,and the strong IEF directional separation of electron hole pair and upress the phonon scattering,resulting in prolonging high-temperature lifetime of intermediate state level for Er³⁺ions.Under980 nm laser,we first observed the thermally enhanced up-conversion luminescence phenomenon of Bi₇F₁₁O₅:Er³⁺,Yb³⁺caused by carrier separation effect,which provides a good idea for solving the traditional existing luminescence thermal quenching.Based on the unique relationship between IEF of Bi₇F₁₁O₅ and luminescence behavior of rare earth ions at high temperature,we selected Eu³⁺ions emitted from the down-conversion far-red light band,up-converted Er³⁺ions in the visible band and Tm³⁺ions in the near-infrared band,and further explored the temperature sensitivity of the rare earth ions of the layered luminescent material,and confirms the feasibility of becoming a"full-function"temperature detector for Bi₇F₁₁O₅.