Preparation And Luminescence Of The Single-host White-light-emitting Phosphor For Ultraviolet LEDs

White-light-emitting diodes?WLED?is a new type of solid-state lighting devices which developed in the last decade.Compared with the traditional incandescence lamps and fluorescence lamps lighting,WLEDs solid-state lighting technology was called the fouth generation of light resource with many advantages,such as energy-saving,higher efficiency,long lifetime,small size and color can be adjusted etc.There are two kinds of approaches to achieve white-emitting LEDs.One is phosphor-converted LEDs?pc-LEDs?in which a single blue/NUV-LED chip is combined with multi-color phosphors,and another is multi-chip combined LEDs with red,green and blue tri-color chips.At present,the main commercialized routine is the phosphors-conversion white LEDs.Hence it is significant to search new type phosphors for InGaN-based WLEDs,both for academic intensity and application.The aim of this thesis is to search for novel phosphors which have high luminescence efficiency and stability for NUV LEDs.In this thesis,a series single-host white-light-emitting phosphor activated by Eu²⁺ and Mn²⁺ for NUV-LED were prepared by high temperature solid-state reaction method.Their crystal structure and luminescence properties of the phosphors were characterized by the modern analytical instruments of X-ray diffraction?XRD?and fluorescence spectroscopy.Respectively,Their excitation spectra,emission spectra and quantum efficiency were also investigated in detail.The thesis consists of the following four chapters.In the first chapter,the principles of white light emitting diode,advantage and its fabrication approaches were introduced.Then the requirements of property and preparation method of the white LED phosphor were discussed.Furthermore,the development of WLEDs and the phosphors for NUV-LEDs were reviewed.To overcome the defects and shortages of the currently used phosphors in "UV-LED +tri-color phosphors",finally,the subject of the thesis is proposed.In the second chapter,a single-host white-light-emitting phosphor BaSrMg?PO₄?₂:Eu²⁺ was prepared by high temperature solid-state reaction method,and the luminescence characteristics and XRD pattern were investigated.The results show that BaSrMg?PO₄?₂ phase was obtain by sintered at 1200? for 3 hours.BaSrMg?PO₄?₂:Eu²⁺ phosphor exhibits two main emission bands peaking at 424nm and 585 nm,respectively.The emission band peaking at 424nm is attributed to the 4f 6 5d¹?4f⁷ transition of Eu²⁺ substituting Sr²⁺,while the emission band peaking at 585nm originates from the 4f 65d 1?4f 7 transition of Eu²⁺ replacing Ba²⁺in host lattice.The excitation spectra of the two emission peaks are range from 250 nm to 400nm and both peaking at 360nm.The effect of the proportion of Ba and Sr,the Eu²⁺doping concentration on the emission intensity are discussed in detail.Different chromaticity coordinates are obtained for each phosphor,that is,the chromaticity coordinates of the designed phosphor is tunable for the white-emitting LED or for special purpose.Quantum efficiency is also examined for the phosphors with different Eu²⁺ doping concentration,and concentration quenching is taken place obviously when Eu²⁺ doping concentration lager than 6%in mole ratio.The obtained phosphor BaSrMg?PO₄?₂:Eu²⁺ can be excited by near ultraviolet radiation effectively and emit full color lighting,which is a promising single-host white-light-emitting phosphor for white LED.In the third chapter,to overcome the shortage of the relatively weak red-emitting of BaSrMg?PO₄?₂:Eu²⁺ phosphor and improve the quality of white light-emitting,asingle-host white-light-emitting phosphor Ba0.98Sr0.98Mg1-x?PO₄?₂:0.O₄Eu2,xMn²⁺was prepared by high temperature solid-state reaction method,and the luminescence characteristics was investigated.The fluorescence spectra result show that:BaSrMg?PO₄?₂:Eu²⁺,Mn²⁺ phosphor emit white light which possess three main emission bands peaking at 424nm?585nm and 645nm,respectively.The emission band peaking at 424nm is attributed to the 4f 6 5d1?4f 7 transition of Eu²⁺substituting Sr²⁺,while the emission band peaking at 585nn originates from the 4f65d¹?4f⁷ transition of Eu²⁺ replacing Ba²⁺ in host lattice,and the red emission band peaking at 645nm can be attributed to the 4T?6A transition of Mn²⁺ in its electronic configuration of 3d5.The excitation spectra of the three emission peaks are distributed in 250?410nm wavelength range,and their maximum are all located around 360nm.The results show that this phosphor can be excited effectively by the near ultraviolet of the InGaN.The effect of the proportion of PO₄ and BO3,the Mn²⁺ doping concentration on the emission intensity,chromaticity coordinates and quantum efficiency are discussed in detail.Different chromaticity coordinates are obtained for each phosphor,that is,x values of the color coordinates follow the order increases first and then decreases,while the y value is in general conformity with the order of decreasing.The red component is gradually increased,which is due to increasing of the concentration of Mn²⁺ while the Eu²⁺?Mn²⁺ energy transfer,making the blue phosphor component decreases.The obtained phosphors BaSrMg?PO₄?₂:Eu²⁺,Mn²⁺can be excited by near ultraviolet radiation effectively and emit white light,which is a promising single-host white-light-emitting phosphor for white LED.In the fourth chapter,the main research results in this thesis were summarized and a brief prospect on the further research of mentioned phosphors was made.