Preparation and Characterization of Zinc Sulfide based Phosphors

• Main Authors: Tzu-Piao Tang, 唐自標
• Other Authors: Ko-Shao Chen
• Format: Others
• Language: en_US
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/94479935143596786583

博士 === 大同工學院 === 材料工程研究所 === 87 === The objective of this paper is to discuss the preparation of ZnS phosphor powder and their firing atmosphere. In this research, several controlling factors that could affect the phosphor''s luminescence characteristics, such as firing temperatures, atmosphere, firing time and the selection of flux and dopant, were evaluated. When prepare the ZnS phosphor powder using solid-reaction firing, it is important to control the distribution of additives. However, the luminescence characteristics of ZnS is dependent upon the firing atmosphere, temperature and time. It is found that the luminescent property of host lattice changes along with amount of hexagonal phase in ZnS phosphors. The higher the firing temperature, the higher the amount of hexagonal phase can be found in ZnS phosphor. Also, its wavelength will shift toward long wavelength region (449nm R453nm) with higher luminescent intensity. For those content less hexagonal phase, its wavelength will move toward short wavelength region (459nmR 457nm) with lower luminescent intensity. After washing with water, the wavelength of ZnS phosphor will shift to short wavelength region (449nm) and shows better luminescent effect and higher intensity. Blue ZnS phosphors with (Ce) dopant can be formed in inert atmosphere and is known as 5dR4f host lattice luminescence. With the addition of flux, its luminescence increase and wavelength is in the ranges between 446nm-480nm. After washing, the higher the Ce residue in ZnS phosphors, the better the luminescence. But, the remained Chlorine and Sodium were also reduced and affect its luminescence. For ZnS phosphors formed at higher temperature, the loss of Ce can be reduced after washing, and thus, help the formation of defect and amount of ions. Under the equivalent of ionic hole and number of ions, it will increase the luminescence intensity. It was found that ZnS phosphor has the highest luminescence intensity when firing at 950℃ with 0.2 Ce mol% addition. Red ZnS phosphors were fired under reducing atmosphere with the addition of Sm+3. ZnS host lattic self-activation luminescence center was found disappeared under reducing condition. When Sm2O2S exists, it has better Sm characteristic luminescence due to Sm ions transfer between 4f-4f orbital and move from 4G5/2 to 6H5/2、6H7/2、6H9/2. If the stable Sm2O3was formed, the self-activation luminescence center will appear. The role of the addition of flux (LiCl) can determine the exciting energy transformation (photoionization) which will then result in either self-activation or Sm characteristic luminescence. A certain amount of LiCl addition can react with Sm compound and increase luminescence intensity. The optimal conditions to form ZnS phosphors with red characteristic luminescence is found at 1050℃ reducing atmosphere and LiCl：2.0 mol％，Sm +3：0.30mol%. The Tb characteristic luminescence was not found in ZnS phosphors when firing under reducing atmosphere with the additon of Tb. This is believed to be due to the Tb characteristic luminescence can only be emitted from5D4→7F6（487nm）、7F5（546nm）、7F4（588nm）、7F3（617nm）green luminescent materials. In order to produce Tb characteristic luminescence, the Tb need to be evenly distributed with the addition of flux. The optimal conditions for this process are 1050℃ firing temperature, reducing atmosphere, 0.5mol% of Tb and KF which is found need to be added three times as much as Tb.