Photoluminescence Spectroscopic Study of BaMgAl10O17:Eu Phosphor Coated with CaF2 via a Sol-Gel Process

CaF2 coatings on the surface of BaMgAl10O17:Eu (BAM) were prepared by a sol-gel process, and the optical properties and antithermal degradation properties were analyzed by photoluminescence spectra recorded under 254？nm and 147？nm excitation. The results indicate that BAM particles were successfully coated with CaF2 and CaF2 coatings show an interesting property to enhance the blue emission intensity of BAM. The optimum antithermal degradation properties were obtained at the weight ratio 0.4？wt% under 254？nm excitation and 0.3？wt% under 147？nm excitation, respectively. 1. Introduction BaMgAl10O17:Eu (BAM) is widely used in plasma display panels (PDPs) and lamps, due to its high luminescence efficiency and good chromaticity [1] and also used in other displays and lighting devices, for example, white light-emitting diodes (WLED). However, luminance degradation of BAM, consisting of thermal degradation and lifetime degradation, restrains the application of BAM, especially in PDPs. In lamps, the degradation of BAM is mainly caused by thermal treatment during lamp manufacturing. In WLED, similar thermal degradation is also observed in BAM and Eu2+ activated nitride-based phosphors [2]. Thermal degradation occurs when the phosphors are heated to about 500–700°C in ambient atmosphere during the manufacturing of PDP and lamps, while in WLED thermal degradation is caused by the heat released by the operating devices. It is generally considered that the luminescent center Eu2+ is oxidized to Eu3+ [1–3]. However, some other potential mechanisms were proposed recently which are related with O2？ incorporated into the crystal lattice of BAM [4–6]. Lifetime degradation is caused by VUV radiation and ion sputtering during PDP operation, which can be explained by the formation of an amorphous surface layer [3]. One of the options to enhance thermal stability and ion resistance in BAM is the application of a closed particle coating [7]. Up to now, several inorganic materials have been reported to be selected as the coating materials such as SiO2 [8, 9], SrO, MgO [7, 10], Al2O3 [8, 11], AlPO4, and LaPO4 [12] and so forth. However, most of them possess strong band gap absorption in the range of 140 to 200？nm, which would thereby cause the reduction of the phosphor efficiency. Thus the option is narrowed to metal fluorides which have a wide transparency range in VUV region and high secondary electron emission coefficient which can improve the pixel brightness [7, 13]. Metal fluorides can be deposited onto the phosphor surface by conventional precipitation or