Structure and Optical Properties of Oxynitride Phosphors

• Main Authors: Wei-Ting Chen, 陳韋廷
• Other Authors: Ru-Shi Liu
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/79533519568174584522

博士 === 國立臺灣大學 === 化學研究所 === 101 === This study focuses on the development of an effect of cation-size mismatch strain between the dopant (activator) and substituted objective (cation in host lattice). Several chemical tunings have been reported; however, their underlying mechanisms remain unclear. In addition, these chemical tunings invariably shift the energy in a group of comparable materials in the same way, e.g., a consistent red shift. Our materials, M2Si5-xAlxN8-xOx:Eu (M = Ca, Sr, Ba), show a large red shift for M = Ba and a small red shift for Sr, but exhibit a large blue shift for Ca. Thus, we propose a mechanism for this size mismatch tuning based on local nitride/oxide anion clustering and supporting evidence. Thermal quenching of photoluminescence is also tuned by cation mismatch, Moreover, both effects are important for light-emitting diode (LED) devices, and both mismatch tuning effects are explained by our size-driven anion clustering model. In the second part, an unreported phenomenon for tuning the emission properties of Tb3+ activators is discussed. Our material, Ba2.89Si6O12N2:Tb0.11, shows the tunable and reversible properties in the green/blue emission under UV to VUV radiation excitation. Thus, we propose a possible mechanism for this color reversal control based on a specific transition route as a color-tunable switch at the UV/VUV range and supporting evidence. This effect is significant for Tb-activated phosphors in PDP or fluorescent lamp devices, and the color-reversal effect is explained by our configurational coordinate model. In the third part, we develop a highly efficient green phosphor for using in a practical UV-LED device. The highly efficient Ba3Si6O12N2:RE (RE = rare earth metal) is composed of single-doped and co-doped phosphors with Eu and Ce rare earth metals. The possible mechanisms of the two important photoluminescence properties are proposed for LED device-used phosphors, namely, (1) spectral shift in a high temperature environment in the Eu-doped phosphor and (2) highly efficient transfer property in the Ce/Eu co-doped analogue. The UV-WLED device is fabricated by green Eu-doped Ba3Si6O12N2 and other blue and red phosphors. The distinctive properties of this oxynitride parent structure make it an interesting subject for research and as a candidate for a blue/green component for UV-LED applications.