Synthesis of novel blue phosphor $(Sr_{1-x}, Ca_x)_2 (B_{1-y}, Al_y)_5 O_9 Cl:Eu^{2+}$ for CCFL and their luminescence properties

Abstract

Cold Cathode Fluorescent Lamps (CCFLs) have a lot of advantages such as excellent white light source, low cost, high efficiency and stable and predictable operation. Due to these properties, CCFLs are often used as LCD display backlight. The most widely used white CCFL lamp phosphors have been compounded for good color rendering when used as an LCD display backlight. These phosphors are referred to as RGB, being composed of Red-Green-Blue fluorescent compounds mixed in the appropriate ratio. $BaMgAl_{10}O_{17}:Eu^{2+}$ (BAM) and $(Sr,Ca,Ba,Mg)_5(PO_4)_3Cl:Eu^{2+}$ are used currently as a blue emitting phosphor in CCFLs application. However, these phosphors have some disadvantages with include low color reproducibility, low thermal stability and brightness. Hence there is urgent need to develop new and novel blue emitting phosphors with high efficiency. Borates have long been used as matrices for luminescent materials. Recently more attention has been turned to halo borates for better properties, and $M_2B_5O_9X$ is discovered to be a noticeable material. Because of the rigid structure and blue light emitting under 254nm excitation from $Eu^{2+}$ activated alkaline metal compounds $M_2B_5O_9X$, this series materials is selected as the candidate. At first, $Sr_2B_5O_9Cl:Eu^{2+}$ phosphor, for CCFLs application was introduced. $Sr_2B_5O_9Cl$ among halo borates materials having high brightness was selected as a host lattice and $Eu^{2+}$ were also incorporated in this material to show blue emission. The reaction temperature and activator concentration as important factors for efficient phosphors were systematically varied to find optimum synthesis condition. Under the optimized synthesis condition, the phosphors synthesized by solid state reaction method showed strong absorption band in UV region (254nm) and high emission intensity (130% of $BAM:Eu^{2+}$). The optimum sintering condition were two-steps sintering procedure, 400℃ for 1 hour, and 800℃ for 2 hours. T...