Study On Luminescence Properties And Applications Of Single-phase Tunable Silicate Phosphors

White light emitting diode（WLED）,as a new generation of green lighting source,has attracted much attention to its advantages of energy efficiency,long operation time and rich color.As an important part of WLED,phosphor directly determines the spectral characteristics of the device and it is one of the key technologies for the development of WLED.The white light obtained from the combination of blue LED chips and commercial yellow phosphor Y₃Al₅O₁₂:Ce³⁺has limited its development applications due to high color temperature and low color rendering index.Another way of combining UV LED chips with trichromatic phosphors has energy reabsorption,and the high defect density generated by the introduction of different base materials may dramatically decrease the luminescence intensity and the quantum efficiency of the given devices.Therefore,many researchers began to focus on the synthesis and research of UV-excited single-phase tunable phosphors.This approach avoids the mixing and energy reabsorption of phosphors,and has the advantages of high color rendering index and low color temperature.Silicate has high thermal stability,light stability and light conversion efficiency,and is an excellent phosphor matrix material.In this thesis,the phosphor materials with co-doped and triple-doped rare earth ions were designed and synthesized on silicate substrates.Through a series of characterization and analysis,the physical phases,theoretical calculations,luminescence characteristics,energy transfer mechanisms and device applications of the synthesized phosphor samples are studied in detail.The main studies are as follows:1.A series of Sr₃B₂Si O₈:Tm³⁺/Dy³⁺/Eu³⁺phosphors were synthesized by high-temperature solid-phase method,and the structural properties,luminescence performance,energy transfer and color modulation of the phosphors were systematically investigated.The crystal structures and the elemental content of the samples was analyzed by XRD,Rietveld structural refinement,and EDS.The energy bands and density of states of the matrix were analyzed in combination with first-principles calculations.The energy transfer process and mechanism from Tm³⁺to Dy³⁺and Dy³⁺to Eu³⁺were discussed in depth based on various theoretical models and calculation methods,and the white light emission is realized by adjusting the ratio of rare earth ions.2.A series of Ce³⁺,Tb³⁺,Sm³⁺triple-doped Ca La₄（Si O₄）₃O phosphors were synthesized by high-temperature solid-phase method.The crystal structures,energy bands and density of states were analyzed by XRD,Rietveld structural refinement and first-principles calculations.In the triple-doped system,the energy transfers process of Ce³⁺→Tb³⁺→Sm³⁺with Tb³⁺ions as a bridge is discussed by the analysis of emission spectra,fluorescence lifetime and chromaticity coordinates.It is also accompanied by a part of the non-radiative energy transfer of Ce³⁺→Sm³⁺.By regulating the concentration ratio of Ce³⁺/Tb³⁺/Sm³⁺ions,multiple emission colors of phosphors can be obtained and eventually white light emission can be achieved.Finally,LED devices were fabricated and tested for their thermal stability,color temperature,and color rendering index properties.