The mechanism of enhancement on the low voltage cathodoluminescence (CL) efficiency by addition of In 2 O 3 in the phosphor particles has been investigated. The effect of In 2 O 3 coating by the sol-gel method on the CL of ZnGa 2 O 4 :Mn phosphors improves the luminance of low voltage CL noticeably. Especially it is observed that the emission intensity for the phosphor ZnGa 2 O 4 :Mn coated with 2 wt % In 2 O 3 is about four times higher than the as-it-is (non-coated In 2 O 3 ). Contrary to low voltage CL, the photoluminescence intensity of In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphors decreases with an increase in In 2 O 3 coating wt %. It is shown by Rutherford backscattering study that the surface distribution of In 2 O 3 on In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphors is islandlike but not intermediate-like (islands on a uniform layer). Also, investigations performed on the electrical conductivity of the phosphor screen prove the In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphor screen to be an insulator. From the present work, it is understood that In 2 O 3 in the phosphor particles probably act as the localized bridge in draining the accumulated charge on the phosphor surface down to the indium tin oxide substrate due to the formation of the localized electrically conductive channels.
The mechanism of degradation on the low voltage cathodoluminescence ͑CL͒ efficiency of SrTiO 3 :Pr,Al,Ga phosphors is investigated. The effect of carbon overlayer adsorbed on the phosphor surface from the vacuum ambient during the electron irradiation done in a high vacuum chamber causes a rapid degradation of low voltage CL noticeably. Especially, based on Auger electron spectroscopy combined with CL spectroscopy it is observed that there is obvious correlation between carbon buildup and loss of CL brightness of the phosphors characterized in this study. Also, it is shown that the increased amount of carbon adsorbed during the electron irradiation on the SrTiO 3 :Pr,Al,Ga phosphor surface is completely removed by heating the degraded SrTiO 3 :Pr,Al,Ga samples at 470°C for 30 min in air. Furthermore, the decreased CL intensity of degraded samples is recovered up to that of original ones together with the removal of carbon. From the present work, it is understood that the rapid degradation of low voltage CL of the SrTiO 3 :Pr,Al,Ga phosphors is directly related to the formation of the carbon overlayer, but not related to a change in the emission properties of the luminescent center themselves.
We have investigated the mechanism of degradation of the low voltage cathodoluminescence (CL) efficiency of SrTiO3:Pr,Al,Ga phosphors. Based on Auger electron spectroscopy and x-ray photoelectron spectroscopy study, it is understood that prolonged irradiation of the phosphor with an electron beam of low voltage and high current density causes characteristic changes [(1) accumulation of overlying carbon and (2) reduction of oxygen] to occur on the phosphor surface. These changes are responsible for the rapid degradation of low voltage CL of SrTiO3:Pr,Al,Ga phosphors. The two aforementioned changes are shown to impact CL output in an important way. An accurate accounting of the total impact of the two changes warrants assessment of the importance of other degradation mechanisms. These other degradation mechanisms include both carbon- and noncarbon-related enhanced nonradiative electron-hole recombination at surfaces.
A nanoscale continuous coating of In 2 O 3 on phosphors for low-voltage display applications is proposed in which the electrical conductivity of phosphor screen plays a major role. The effect of In 2 O 3 coating by the sol-gel method on the cathodoluminescence (CL) of ZnGa 2 O 4 :Mn phosphors improves the intensity of low-voltage CL noticeably compared with that of In 2 O 3 mixing. It is understood that electrically conductive channels are formed by a much smaller amount of In 2 O 3 addition than that of In 2 O 3 mixing. Especially, based on transmission electron microscopy analysis, the formation of uniform nanoscale continuous In 2 O 3 layers on the phosphor surface was confirmed. Also, the structural and CL characterizations presented in this paper clearly demonstrate that the nanoscale encapsulation of In 2 O 3 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.
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