Study on fluorescence of Na2KSb(Cs) multi-alkali photocathode film during growth process

This paper describes the measurement principle of fluorescence spectrum on Na2KSb film of multi-alkali photocathode and three samples were measured in the position of different radius. The data resulted shows that the peak wavelength of fluorescence spectrum on Na2KSb film from center to edge of the photocathode surface gradually increased, while the peak fluorescence intensity gradually increased as well. The reason is that the antimony atom density of photocathode surface from the center to the edge gradually reduced. When the antimony in Na2KSb film exceeds stoichiometry required, the fluorescence peak wavelength shifts towards the short-wave direction, while the fluorescence intensity decreased at the same time. When the antimony in Na2KSb film achieves stoichiometry required, the fluorescence peak wavelength reaches the maximum value, while the fluorescence intensity reaches the strongest at the same time. By fluorescence test one can judge whether the stoichiometry of Na2KSb film reaches to the ratio 2:1:1 or not, in another words whether antimony in Na2KSb film is overdose or not. In addition by measuring the fluorescence spectra at different positions of the photocathode surface, we can measure component uniformity in the Na2KSb photocathode film. The more uniform antimony atom density is in the photocathode surface, the more accurate the monitor method of film growth by measuring changes of the photocathode photocurrent is, thus component uniform can be better, Na2KSb film thickness can be thicker, long-wave absorption of visible light is more, the sensitivity of the photocathode is higher. Therefore, during the manufacturing process of multi-alkali photocathode of image intensifier, one has to make the uniform antimony atoms density on photocathode window surface in order to achieve higher sensitivity.