In spite of recent frequent researches on the role of $In_2O_3$ on the phosphor surface, there are many ambiguous corners on its mechanism of improving cathodoluminescence. In this study basic experimental results of the low- voltage CL properties, electrical conductivity, and surface distribution of $In_2O_3$ on $In_2O_3$-coated $ZnGa_2O_4$:Mn phosphors are presented. Also, the role of $In_2O_3$ is suggested.
The synthesized $ZnGa_2O_4$:Mn phosphor was coated with $In_2O_3$ by hydrolysis of indium-iso-propoxide [$In(OCH(CH_3)_2)_3$] with varying the concentration by the sol-gel process. The range of weight% of $In_2O_3$ coating on phosphors was from 1 to 5%. The effect of $In_2O_3$ coating by the sol-gel method on the CL of $ZnGa_2O_4$:Mn phosphors improves the luminance of low-voltage CL noticeably. Especially it was observed that $ZnGa_2O_4$:Mn phosphors coated with 2wt.% $In_2O_3$ showed the optimum CL intensity. Furthermore, it was shown by RBS study that the surface distribution of $In_2O_3$ on $In_2O_3$-coated $ZnGa_2O_4$:Mn phosphors is island-like but not intermediate-like(island on a uniform layer).
The CL test and the measurement of electrical conductivity of $In_2O_3$(2wt.%)-coated samples with the variation of heat-treatment were performed to know how $In_2O_3$-island influenced the low-voltage CL properties. Consequently, from this study it is understood that the $In_2O_3$-islands on the $In_2O_3$-coated $ZnGa_2O_4$:Mn phosphors may act as recombination centers for electron-hole pairs.
