Study On The Surface Coating Of The Near-UV Emitting Phosphor

Lead-activated BaSi₂O₅ (BaSi₂O₅:Pb, BSP) is mainly used as the long wavelength Ultraviolet (UV) phosphor in the suntanning lamps, as well as some special lamps for diazo-printing reprography, lithography, insect traps, photochemical and curing processes. A well-known problem of BSP is the poor radiance maintenance in a fluorescent lamp. An Al₂O₃ coating by CVD (Chemical Vapor Deposition) method onto the phosphor particles of BSP is one effective process to improve the radiance maintenance of the phosphor. However the CVD process is more expensive than the common solution based one. Therefore, the main purpose of this thesis is to study and to develop a solution based method for Al₂O₃ coating onto the BSP phosphor.In the first chapter of this thesis, the categories of the Ultraviolet (UV) radiation, the applications of UV radiation, the luminescent mechanism of some commercial UV-emitting phosphors, the applications of UV-emitting phosphors, the prevalent processes of surface coating onto the phosphor particles and the influence of the surface coating on the UV phosphor's, as well as on the UV lamp's performance were introduced briefly.In the second chapter of this thesis, six samples of BSP phosphors produced by some oversea and domestic companies were investigated by means of SEM (Scanning Electron Microscope), XRD (X-Ray diffraction), XRF (X-Ray Fluorescence), fluorescent spectrophotometer and light test, respectively. The results showed that the surface of BSP phosphor from oversea company was coated by a film of nanometer Al₂O₃ particles. Other performances of BSP phosphors indicated that there was a large gap not only in the initial output but also in the lumen maintenance between the oversea BSP phosphors and the domestic BSP phosphors.In the third chapter of this thesis, we developed a wet-chemical method that could be carried on at a condition of high pH value and was thus harmless to the BSP phosphor. This method was composed of following procedures: adding an amount of a silicate phosphor to a salt solution containing a cation, such as Ba2+, stirring the...