Nanoscale continuous In 2 O 3 coating on phosphor particles for improved low-voltage cathodoluminescent properties
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Il Yu Department of Physics, Dong-Eui University, Busanjin-Gu, Busan 614-714, Republic of Korea (Received 10 October 2002; accepted 17 March 2003)
A nanoscale continuous coating of In2O3 on phosphors for low-voltage display applications is proposed in which the electrical conductivity of phosphor screen plays a major role. The effect of In2O3 coating by the sol-gel method on the cathodoluminescence (CL) of ZnGa2O4:Mn phosphors improves the intensity of low-voltage CL noticeably compared with that of In2O3 mixing. It is understood that electrically conductive channels are formed by a much smaller amount of In2O3 addition than that of In2O3 mixing. Especially, based on transmission electron microscopy analysis, the formation of uniform nanoscale continuous In2O3 layers on the phosphor surface was confirmed. Also, the structural and CL characterizations presented in this paper clearly demonstrate that the nanoscale encapsulation of In2O3 layers on phosphors served as protective layers retarding the CL degradation introduced by the low-energy electron irradiation, which is critically important for the development of low-voltage display applications.
I. INTRODUCTION
There exist a number of special requirements to be specified for the low-voltage cathodoluminescent phosphor screens for low-voltage display applications such as field-emission displays or vacuum-fluorescent displays.1–3 Especially, the charge removal from the screen through the phosphor layer is of great technological importance for such display devices because aluminizing these phosphor screens developed for cathode-ray tubes cannot be used. A usual method to solve this problem is to mix conductive materials such as SnO2, WO3, ZnO, In2O3, and so forth to the phosphor particles. Among these listed, In2O3 is used as one of the most effective conductive materials because of the high luminous efficiency it offers.4 Usually, when the mixing amounts of In2O3 are about 10–15 wt.%, optimum cathodoluminescence (CL) intensities are obtained. It is known that In2O3 provides adequate screen conductivity, resulting in a significant improvement in the phosphor performance, especially at low voltages.5 However, the density of the conductive In2O3 particles is much larger than that of phosphor particles; also, the particle size of the former is much smaller than that of the latter. Thus, in the case of a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 7, Jul 2003
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In2O3-mixed phosphor screen, it is true in an early stage of operation of the device that phosphor and In2O3 particles in the screen are uniformly mixed, but In2O3 particles go down to the indium tin oxide (ITO) substrate of the screen by the aforementioned difference in the two kinds of particle as time passes by. Eventually, many In2O3 particles are separated from phosphor particles, which leads to the instability of the conductivity of the phosphor screen and thereby deteriorates the uniformity an
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