Eu- doped α-SiAlON phosphor First-principles study
|School||University of Science and Technology of China|
|Keywords||Ca-α-SiAlON Mg-α-SiAlON Photoluminescence First-principles calculations|
In 1996, in Japanese Nichia GaN blue LED (light emitting diode, light-emitting diode), based on development of a light-emitting diode device (white LED) can be used as a lighting device. White LED and traditional incandescent and fluorescent lighting devices have many advantages compared to, for example, small size (small particles, the combination of convenience), low power consumption, low heat dissipation (no heat radiation), long life (theoretically more than 100,000 hour), fast response, environmental pollution (non-polluting, recyclable), thus giving rise to an R \u0026 D white LED boom. The light from the semiconductor material principle known, a single LED chip emits a continuous spectrum of white light is difficult. It is generally three ways to achieve white light: (1) three-color red, green and blue LED, mixed to form white light, but the technology and control system is relatively complex; (2) may be a blue LED and a blue light excitation of red, green phosphor (or yellow phosphor) in combination, in this process the LED emits blue light, can be absorbed by the phosphor, and generate red, green (yellow) light, blue light is not absorbed and is absorbed by the phosphor and the excitation produce red, green or yellow mixed to produce white light, thus avoids UV damage to the eyes, but also reduces the loss of light energy conversion process; (3) and similar tricolor energy-saving lamps, using near-ultraviolet LED, can be effectively stimulate red, green, and blue phosphors organic combined to produce white light. Theoretically this technique can be formulated into any color temperature of a light source, and its color is better, easier to prepare. White LED phosphor development is one of the key development. Most of the conventional matrix aluminate phosphor, sulfide, silicate, and the like. In recent years, there have been many foreign to the silicon nitride substrate and nitrogen oxide, and rare-earth doped fluorescent material reports, such as M-α-SiAlON: Eu 2 sup> (M = Li, Mg, Ca, Y), Sr2Si5N8: Eu 2 sup> and so on. Nitrides and oxides of nitrogen and sulfur oxides with respect, because nitrogen has a relatively small electronegativity and larger electron cloud expansion effect, the effective promotion 5d levels of rare earth ions in the crystal field splitting, thus the 5d-4f energy difference between the reduced excitation - emission wavelength redshift, and ultraviolet or blue LED match. While a wide range by adjusting the ratio of oxygen to control the excitation of nitrogen - emission wavelength, the phosphor having more excellent controllability, improve the performance of the white LED, while the nitrogen oxides of nitrogen also has stable chemical properties and excellent Gao Wen Faguang performance. α-SiAlON is the first to propose a silicon oxynitride phosphor. In the experiment found that different interstitial matrix metal ion luminescence affected, such as Ca-α-SiAlON light conversion efficiency greater than Mg-α-SiAlON, but through the general theory is difficult to give a light-emitting reasonable explanation. This thesis work is to combine experimental measurements density functional theory calculations to study the impact of interstitial metal ion mechanism of the optical properties of the phosphor. Since Ca and Mg have the same valence, for purposes of comparison, we chose Eu-doped Ca-α-SiAlON, and Mg-α-SiAlON the study. The first chapter introduces the application of white LED and white LED phosphors and phosphor for first-principles electronic structure calculations. The second chapter describes the study M-α-SiAlON: Eu 2 sup> nature means that there is an X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and calculation software Materials Studio. XRD analysis of different methods for the preparation of the crystalline quality of the material; SEM surface morphology for materials characterization; PL spectra mainly used to study the optical properties of materials; calculation software Materials Studio is built to calculate the crystal structure of the material species in nature. Chapter Three experiments were prepared by the Eu-doped Ca-α-SiAlON and Mg-α-SiAlON, and studied their photoluminescence spectra. The results showed that, Ca stable α-SiAlON and Mg stable α-SiAlON, the light intensity are different. Then we build a reasonable structure model, these two structures were calculated electronic density of states and band structure, density of states through the analysis of the results found that Ca and Mg compared to the bottom of conduction band contribute more, and in the two structures, the valence band is mainly the contribution from Eu4f electronic states, which can be explained qualitatively Eu, Ca-α-SiAlON better reason luminescence properties.