Growth And Luminescence Properties Of Rare Earth/Transition Doped Na₅Lu₉F₃₂ Fluoride Single Crystals

With the development of science and technology,luminescent materials have been widely used in defense military applications,white LEDs,optical storage and optical communication.It has become a hot research field to seek efficient and stable luminescent materials.The luminescent activation centers of the luminescent materials are mainly rare earth ions and transition metal ions.Due to the unique structure of the electronic laye r and the large number of energy levels,rare earth ions have become one of the ideal combinations of luminescent materials.These luminescent materials have excellent optical properties and have strong practical application potential.Unlike rare earth io ns,d electrons derived from transition metal ions are exposed to the outside,and are not shielded by outer electrons like rare earth ions 4f electrons,resulting in a large phonon-electron coupling coefficient,and thus are more sensitive to the chemical environment of the parent material.The chemical environment of the parent material can effectively adjust the luminescent properties of the transition metal material.In this paper,Cr³⁺,Pr³⁺,Tm³⁺/Er³⁺/Yb³⁺and Tm³⁺/Tb³⁺/Yb³⁺doped Na₅Lu₉F₃₂ single crystals were grown by an improved Bridgman method.The crystal structure was determined by testing and analyzing XRD diffraction patterns,and its luminescence properties and mechanism were characterized by absorption spectra,excitation spectra,emission spectra,fluorescence decay lifetime,external quantum efficiency,pump power density and energy level diagram.The introduction of this article introduces the background of the subject,the development status of rare earth/transition luminescent materials,laser crystals and white LEDs.The crystal structure and unique optical properties of Na ₅Lu₉F₃₂ single crystal are briefly introduced,and the preparation method of Na₅Lu₉F₃₂ single crystal is described in detail.In the second chapter,the Cr³⁺single-doped Na₅Lu₉F₃₂ single crystal was grown by the modified Bridgman method.The crystal structure and luminescence mechanism of Cr³⁺doped Na₅Lu₉F₃₂ single crystal were analyzed by XRD diffraction,absorption spectra,excitation spectra and emission spectra.The results show that the crystal emits red light at670 nm under the ultraviolet light of 259 nm,and the red light at the wavelength of 550-670 nm can promote the repair of the skin barrier.Red light has high purity,strong light source,and even energy density.It has a significant effect on skin care and is called biologically active light.It is harmless to the skin and has potential applications in cosmetic lasers.In the third chapter,the growth of Pr³⁺-doped Na₅Lu₉F₃₂single crystals by the modified Bridgman method is reported.The absorption spectra,emission spectra and lifetime decay curve of Pr³⁺-doped Na₅Lu₉F₃₂single crystals are systematically studied.Judd-Ofelt analysis performed on the obtained crystal reveals that the Pr³⁺ions are exposed to a high symmetric environment with strong degree covalency of Pr-F bond.The sharp and strong emission bands centered at 482,523 and 605 nm are observed under 440 nm excited.The effects of the temperature on the emission spectra of the Pr³⁺doped single crystal have been investigated in detail.The fourth chapter studies the Cubic Na₅Lu₉F₃₂ fluoride single crystals tri-doped with various Tm³⁺/Tb³⁺/Yb³⁺concentrations were grown by an improved Bridgman method.The absorption spectra and fluorescence spectra of Tm³⁺/Tb³⁺/Yb³⁺tri-doped Na₅Lu₉F₃₂single crystal were studied systematically.The colors of up-conversion(UC)luminescence could be tuned effectively by adjusting both the doing rare earth ion concentration and the excitation laser power.The fifth chapter studies Yb³⁺,Er³⁺and Tm³⁺tri-doped Na₅Lu₉F₃₂single crystals with various dopant concentrations were prepared by Bridgman method.Under 980 nm laser excitation,the Tm³⁺/Er³⁺/Yb³⁺tri-doped Na₅Lu₉F₃₂single crystals exhibit strong red,green emission and relatively weak blue light,which is ascribed to the sensitization of Tm³⁺to Er³⁺and Er³⁺acts as quenching center for the blue up-conversion luminescence of Tm³⁺ions.The red and green up-conversion are consistent with ⁴F_9/2?⁴I_15/2 and ²H_11/2,⁴S_3/2?⁴I_15/2 transition of Er³⁺,respectively,while the blue up-conversion originates from ¹G₄?³H₆transition of Tm³⁺.Up-conversion blue,green and red emissions were investigated as a function of the excitation power to determine the necessary photons number for the energy transfer processes from Yb³⁺to Er³⁺and Tm³⁺ions.The sixth chapter of the thesis is a summary,and further prospects and expectations for the follow-up work.