First Principles Study On AlON Based Fluorescent Materials

White LED is a new generation of energy-efficient light source,which is widely used in solid state lighting and display.The single-host tricolor phosphor and near ultraviolet(NUV)LED combination holds promise for obtaining white LEDs.Particularly,y-AlON shows a cubic spinel structure with excellent thermal stability and chemical stability,which make it a promising host material for the development of advanced phosphors.A high internal quantum efficiency and tunable chromaticity coordinates make AlON:Eu2+blue phosphor a suitable candidate for white LED applications.(1)In this work,the crystal structural of γ-AlON host was firstly calculated to understand the crystal structure from theory aspect.Then,the electronic structure and optical properties of Eu2+doped γ-AlON were studied.The luminescence properties and mechanism of Eu2+doped γ-AlON were discussed based on the calculated results.Finally,the influence of co-doping of Eu2+,Mn2+andEu2+,Mg2+ on the electronic structure and optical properties of AlON:Eu2+wereinvestigated.(2)The structure model of AlON was established on related experimental data with virtual crystal approximation.The calculated results shows that Al23O27N5 host has a large band gap(4.03 eV),which is a favorable property for luminescent ions.AlON:Eu2+phosphor exhibits a direct band gap,which is advantageous for luminescence.AlON:Eu2+presents an intense absorption in the range 275-425 nm with a maximum at 335 nm,which was assigned to electronic transitions from the 4f7 levels to the 4f65d1 levels of Eu2+.Accordingly,The absorption spectrum of AlON:Eu2+ is consistent with corresponding experimental excitation spectra,which matches well with the excitation spectrum of InGaN LED.(3)Investigation of the Eu2+sites shows that doped Eu2+ prefers to occupy the VAlO5N site,which is an octahedral vacancy coordinated by five oxygen ions and one nitrogen ion.The lattice parameters and primitive cell volume of EuxAl23-xO27N5 increase with increasing Eu2+concentrations.The existence of Eu-N bonds enhanced the local covalence of Eu2+,hence the optical stability of AlON:Eu2+ phosphor.(4)In this thesis,Co-doping in AlON based fluorescent materials wereinvestigated,the energy transfer mechanism in AlON:Eu2+,Mn2+were confirmed by theoretical calculation.Accordingly,the absorption intensity of AlON can be effectively improved with the codoping of Eu2+and M(M=Mn2+,Mg2+,Li+),which resulting in a red shift with respect to the absorption spectrum of AlON:Eu2+.The absorption peaks of AlON:Eu2+,Mn2+and AlON:Eu2+,Mg2+are located at 357 nm、369 nm respectively,while the absorption peaks of AlON:Eu2+is located at 335 nm.(5)The optical properties of AlON:Eu2+,Li+were predicted by theoretical calculation.The absorption peak of AlON:Eu2+,Li+reaches at 67266 cm-1,which located at 357 nm in the range of 275-415nm.Particularly,the absorption intensity of AlON:Eu2+,Li+is significantly higher than that of AlON:Eu2+in ultraviolet blue light region.As an novel AlON based fluorescent material,AlON:Eu2+,Li+should be weedly applied in ultraviolet excited white LED.