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White illumination characteristics of ZnS-based phosphor materials excited by InGaN-based ultraviolet light-emitting diode

White illumination characteristics of ZnS-based phosphor materials exited by an InxGa1-xN-based single quantum well-structure ultraviolet (UV) light-emitting diode (LED) have extensively been investigated. In order to evaluate white luminescence, two kinds of ZnS-based white phosphors have been employed. When an UV LED was operated at a current of 10 mA, chromaticity (x, y) color temperature (Tc) and general color rendering index (Ra) of the white luminescence are obtained to be (x,y) equals (0.29, 0.33), Tc equals 7700 K and Ra equals 70, respectively, for ZnS:Ag + (Zn,Cd)S:Cu,Al phosphors, whilst (x,y) equals (0.31, 0.34), Tc equals 6900 K and Ra equals 83, respectively, for white phosphor material including ZnS:Cu,Al, Sr and Y materials. The value of chromaticity slightly changed with increasing forward current of the UV light source. As a result, it is possible to obtain stable white luminescence spectrum. The dependence of the luminescence brightness on the thickness of phosphor shows a tendency to saturate for reflection brightness, but for transmission brightness its dependence has a peak due to light scattering effect. The reflection brightness was higher than the transmission brightness. It is revealed that the white luminescence light of stable chromaticity and high brightness using reflection light can be obtained.