Thin SiO 2 coating on ZnS phosphors for improved low-voltage cathodoluminescence properties
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Y.R. Do and H.G. Yang Materials Technology Laboratory, Samsung SDI Co., Ltd., 575 Shin-Dong, Paldal-Gu, Suwon City, Kyungki-Do, Korea 442-390 (Received 25 February 2000; accepted 10 August 2000)
A significant improvement (40–60%) was reported in the low voltage (100–1000V) cathodoluminescence efficiency of ZnS phosphors coated with SiO2 by the sol-gel technique. The properties of the coatings were found to be critically dependent upon the precursor concentration, pH value and the temperature of the solution with optimum performance being obtained for a SiO2 concentration of 1.0 wt%, pH values between 7–9, and a solution temperature of 83 °C. The efficiency curves exhibited a characteristic voltage dependence which was analyzed by a one-dimensional numerical model. Enhanced low voltage efficiency was attributed to a reduction of surface recombination and the actual shape of the efficiency curve was determined by the interplay between the reduction of surface recombination and energy losses in the SiO2 coating.
The physical mechanism of phosphor excitation in the field emission display (FED) and conventional cathode ray tube (CRT) displays is the same. However, FEDs operate at much lower voltages, which makes it necessary to use higher current densities in order to maintain the same output luminance.1 At low acceleration voltages, the electron penetration depth is small compared to the phosphor particle size, and therefore, phosphors exhibit low efficiency due to the loss processes associated with the surface. However, there are many advantages that can be achieved by very low voltage (
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