Synthesis And Properties Of Al Nitride Based Phosphors

Excessive energy consumption and serious pollution of environment has become an important problem to be solved. Development of energy-saving and environmental-friendly light source has become an important subject in the lighting and display area. White light LEDs (light emitting diodes) has received the widespread attention due to its energy saving, environmental protection, long life time and high luminous efficacy.The main way to form the white light LEDs is the combination of the blue emitting InGaN chip with yellow YAG:Ce phosphor, but the lack of red component leads to a low color rendering index. The main method to solve this problem is to add a red emitting phosphor, or combine UV LED chips with blue, green and red phosphors. The phosphor plays an important role.Compared to the traditional phosphors, (oxy)nitride phosphors are the most attractive phosphors for white LEDs due to their excellent properties. Nitride phosphor have a great variety of crystal structures and varying local structures surrounding the activator ions, which can make changes in the centroid shift and crystal field splitting of rare earth ions, leading to various emission colors of nitride phosphors. Nitride host lattices are very stable against chemical and thermal attacks, which results in small thermal quenching and degradation of nitride phosphors. With so many excellent optical properties, nitride phosphors are very suitable for use as downconversion phosphors in white LEDs.This dissertation mainly investigated the Al nitride based phosphor, and contains six chapters:Chapter 1 describes the brief history of lighting development, LED technology and rare earth. The phosphors for white LEDs, mainly the (oxy)nitride phosphors, were described.Chapter 2 reports the synthesis of AlN:Eu2+ phosphor andAlN:Ce3+ phosphor by a Sol-Gel method. Use A1(NO3)3 and citric acid as raw materials, The effect of raw materials and sintering temperature on the A1N structure were investigated. The result showed that the A1N phosphors could be acheived with the Al(NO3)3/citric acid ratio of 0.7 and the temperature of 1500℃. Sol-Gel method can get high purity A1N based phosphor, and the Eu2+ and Ce3+ are easy to incorporate into crystal lattice. The emission wavelength of AlN:Eu2+ phosphor is 520nm and the emission wavelength of AIN:Ce3+ phosphor is 430nm. The obtained phosphors contain nano-sized particles with an average diameter of about 200nm.Chapter 3 reports the energy transfer in AlN:Ce3+,Tb3+and AlsO6N:Ce3+,Tb3+. The AlN:Ce3+,Tb3+and Al5O6N:Ce3+,Tb3+phosphors were synthesized through high-temperature solid state reaction. The Ce3+ doping can significantly increased the emission of Tb3+ ions. Efficiency energy transfer occurred in both phosphors, and the energy transfer efficiency was more than 95%. According to Blasse and Dexter, the energy transfer from Ce3+ to Tb3+ are governed by a dipole-dipole interaction mechanism.Chapter 4 reports the synthesis and photoluminescence properties of MAlSiN3.Eu2+(M=Ca, Mg) phosphors. We successfully synthesized the high performance CaAlSiN3:Eu2+red phosphor with the aid of BaF2 flux at 1600℃. In the flux-free sample, CaAlSiN3 forms in a two-step mechanism, Ca3N2 and S13N4 reacts at a lower temperature and then react with the more thermally stable A1N at higher temperature. With the aid of BaF2, the reaction to form CaAlSiN3 occurs in one step at a lower temperature. The the replacement of Ca2+ by Sr2+ and Mg22+ was studied, in terms of the XRD and photoluminescence spectra. MgAlSiN3:Ce3+ blue-emission phosphor was synthesized for the first time, which shows great potential applications inwhite LEDs.Chapter 5 reports the study of Sr1-xCaxLiAl3N4:Eu2+ solid-solutions and their photoluminescence properties. Pure Sr1-xCaxLiAl3N4:Eu2+ phosphor was successfully synthesized under N2/H2 atmosphere by the solid state reaction method. The effects of replacemtn of Sr2+ by Ca2+ were studied in terms of the XRD patterns and photoluminescence properteis. With the increase of Ca2+ content, the emission wavelength exhibits a blue shift. The location of Ca2+ ions was studied theoretically and experimentally.We also found that a small amount of Ba replacement will increase the emission intensity, which provides a simple way to prepare high performance SrLiAl3N4:Eu2+ phosphor.Chapter 6 is the conclusion of this dissertation. The shortcoming was pointed out, and some suggestion for further study have been given.