Study On Rare Earth Doped LiLuF₄ Single Crystal For White Light Emission

Recently,the realization of white light emission（w-LED）by single-host full-color luminescent phosphors such as glass,transparent ceramics and single crystals has attracted attention because it may simplify the packaging process and improve device performance.Nowadays,the rare earth（RE）ion doped transparent materials are almost used phosphors to realize the purpose of single-host full-color emitting.Usually,RE ions have abundant energy level structures and can emit various wavelength lights under the excitation of suitable light sources.However,there are scarce reports on rare-earth ion doped single crystals for w-LED due to the expensive equipment and the technical difficulties in crystal growth.Phosphor converted white lighting-emitting diode is the most prevalent approach in LED-based solid-state lighting industry,in which a highly efficient blue LED is combined with luminescent phosphors to produce white emission.Moreover,light scattering arisen from the refractive index mismatch between phosphors and epoxy should also be considered.Therefore,it is urgent to develop a single-phase full-color emitting phosphor that can be effectively excited by UV light to generate white light efficiently.Furthermore,w-LED based on the single-phase full-color emitting phosphor is advantageous for easy fabrication with excellent stability and color reproducibility than the multiple-emitting components-based w-LEDs.Among various transparent hosts,many single crystals are of good resistance to light exposure,good thermal,mechanical and chemical stability,and the high luminous efficiency of active ions.They were thought to be more favorable single-phase material for high brightness w-LED devices.However,there are scarce reports on rare-earth ion doped single crystals for w-LED due to the expensive equipment and the technical difficulties in crystal growth.Very recently,several single crystals have been grown and white light emission has been obtained in our laboratory.In this work,LiLuF₄ single crystal is chosen as the host for Dy³⁺/Tb³⁺and Dy³⁺/Eu³⁺pair to explore the white light generation.LiLuF₄ is a favorable host for Dy³⁺/Tb³⁺and Dy³⁺/Eu³⁺ions not only due to their high doping concentrations in the single crystal beneficial from their comparable ionic radius and same value state between dopants and Lu³⁺lattice ion,but also high radiative efficiency of the dopants gaining from the small phonon energy of LiLuF₄(440 cm^-1).The introduction part of this paper describes the development and application of LED,introduces the working principle,performance index and classification of LED,and finally expounds the significance of research on the present situation.Chapter one introduces the application of rare earth luminescent materials in solid-state ultraviolet laser and solid-state white light LED,as well as the basic concepts and practical applications of rare earth luminescent materials in some fields.In the second chapter to the fifth chapter,we introduce several experimental results:Dy³⁺/Eu³⁺doped LiLuF₄ single crystal,Dy³⁺/Tb³⁺doped LiLuF₄ single crystal,Pr³⁺doped LiLuF₄ single crystal and Co²⁺doped Na₅Lu₉F₃₂ single crystal.At the end of this paper,the advantages of rare earth ion doped fluoride are summarized,and the future development is prospected.