Preparation And Luminescence Property Of Oxonitridosilicate Phosphor For White Light LED

Since 1996, the Nichia Company developed the white LED based on the InGaN chip. A lighting revolution is sweeping all over the world. The white light LED has many advantages, such as superior lifetime, efficiency, reliability and designable, compared with the fluorescent and conventional incandescent lamps.Due to the luminescent mechanism of semiconductor, one LED chip could not emit white light. There are three fundamental ways of generating white light in white light LED:(1) Combination of red, green, blue-LED chips, but the techniques and controlling system are very complex. (2) Combination of a yellow phosphor with the blue LED chip, such as YAG:Ce3+phosphor and GaN chips. The emission of LED was absorbed by the phosphor, which can reduce the hurt of the ultraviolet radiation and the waste of emission energy. (3) Combination of three primary color phosphors which can be excited by an ultraviolet (UV) LED. This three-converter system is improved in color rendering and directionality, compared to the white light LED composed of a yellow phosphor and blue emission LED. Much interest currently exists in down-converting phosphors for application in white light LED.The phosphor is very important in white light LED. Traditional phosphors usually based on the sulfide, aluminate and silicate. Recently, the rare-earth doped (oxo)nitridosilicate phosphors have attracted much attention, for example Sr2Si5N8:Eu2+, Ca-α-SiAlO:Eu2+. In (oxo)nitridosilicate phosphors, the nephelauxetic effect and the relative low electronegativity value of N3" ion cause the large splitting of 5d energy levels, which make the redshift of the excitation and emission band, so it make them as a potential candidate for the UV-LED and blue LED. The (oxo)nitridosilicate phosphor also have the advantages of better flexibility, composition-tunability and higher thermal and chemical stability. This thesis focuses on the preparation of the new (oxo)nitridosilicate phosphor. We studied their structure, luminescence properties and the potential of application in the white light LED.This thesis consists of five chapters. Chapter 1 introduces the lighting history especially about the White-Light-LED. Chapter 2 is experimental procedure. Chapter 3 and chapter 4 studied the M2Al2Si10N14O4 and MgYSi2O5N based phosphors respectively. Chapter 5 discusses their portential of application in white light LED.In chapter 3, we prepared the Ba2Al2Si10N14O4, Sr2Al2Si10Ni4O4 and Ca2Al2Si10N14O4 based phosphors by solid-state reactions. Their properties were studied in terms of XRD, SEM and light-conversion properties. Following is some conclusions:1. The pure Ba2Al2Si10N14O4 phase could be prepared at 1600℃under latm N2 atmosphere. The excitation band of Ba2Al2Si10N14O4:Eu2+ is located in 300nm and covers the 270nm-350nm region. The emission band is located at 476nm-527nm depending on Eu2+concentrations.2. The Sr2Al2Si10N14O4 can not be prepared at 1600℃under latm N2 atmosphere, but pure Sr2Al2Si10N14O4 phase could be obtained with the addition of only 1 wt%Ba. Compared with the Ba2Al2Si10N14O4:Eu2+, the excitation band of Ba stabilized Sr2Al2Si10N14O4:Eu2+redshifts to 340nm and covers the 280nm-400nm region, the emission also redshifts to the 508-540nm. The reason of redshift is the coordination changed due to the substitution of Ba with Sr.3. Pure Ca2Al2Si10N14O4 can not be synthesized, but the substitution of Ba with Ca can adjusting the photoluminescence properties of Ba2Al2Si10N14O4. The highest Ca incorporation is 20% of Ba based on XRD measurement. In the Ca doped Ba2Al2Si10N14O4:Eu2+, when the Ca occupy the Ba, the crystal field around the Eu2+ changed, which cause the large splitting of 5d energy levels, the energy gap between 5d and 4f energy levels is decreased. So the emission redshifts from 476nm-527nm of Ba2Al2Si10N14O4:Eu2+to 527nm-555nm of 20% Ca incorporated Ba2Al2Si10N14O4: Eu2+ phosphor. Because of the shrinkage of the crystal lattice, the distance between Eu2+ is small, and the probability of energy transfer increases, so the quenching concentration of Eu2+ is smaller.4,The change of x value can adjusting the ratio of O/N, so the luminescence properties of Ba2AlxSi12-xN16-xO2+x:Eu2+ will change with the x value. There is a broad excitation band of Ba2Al6Si6N10O8:Eu2+ which covers 250nm-420nm. The emission band is 470nm and the intensity of emission nearly twice higher than the YAG:Ce3+. In chapter 4 we synthesized the MgYSi2O5 by the solid-state reaction method and studied the luminescence properties of MgYSi2O5:Ce3+, Mn2+phosphors. We discovered that:1. There were two excitation bands in the MgYSi2O5:Ce3+, which located 289nm and 324nm respectively. There is a blue doublet emission band at 400nm. The doublet emission due to transitions from the lowest 5d level to the 2F5/2 and 2F7/2 spin-orbit split 4f ground state level of Ce3+.2. We studied the luminescence properties of MgYSi2O5N:Ce3+,Mn2+, there are blue and red emission bands at 400nm and 600nm-700nm respectively while there is only blue emission band in the MgYSi2O5N:Ce3+, it confirms the effective resonance-type energy transfer from Ce3+to Mn2+. The excitation spectra of both phosphors composed of a double excitation bands and redshift occurs with the incorporation of Mn2+. We also discovered that the Mn2+ can enhance the blue emission of Ce3+. There are two emission bands of Mn2+, one is located at 603nm and the other is located at 672nm. The 602nm emission dominates at low Mn2+ concentration, while the 673nm band dominates at higher Mn2+concentrations, due to the energy transfer between Mn2+ions.3. The luminescence properties of Lu3+or Zn2+ doped the MgYSi2O5N:Ce3+, Mn2+ phosphors were also studied.In chapter 5, we concluded the previous results, and studied how to obtain white light by the combination of the Sr2Al2Si10N14O4:Eu2+and MgYSi2O5N:Ce3+, Mn2+ phosphors with a UV-LED.