A new preparing process of photoconductive CdSe powders suitable for an EL-PC-type X-ray image converting panel was proposed.The influence of parameters such as amount of flux and activator in the raw mixture, firing temperature and firing atmosphere on the photoconductive characteristics was investigated. To keep the amount of flux minimum was not only effective to improve the photosensitivity, threshold voltage and granularity of resultant photoconductive powders but also effective to make the preparing process simple and reliable.Applying such improved photoconductive powders to a solid-state X-ray image converting panel, the brightness and resolution of the panel was remarkably improved.
The preparation and properties of direct current electroluminescent (dc EL) materials using manganese-activated ZnS powders for a flat-panel TV display are described. The firing process, the copper coating process, and the ferming process have been investigated. Suitable powder phosphors for the display panel contain 0.1-0.5 wt % manganese and 0.25-0.35 wt % copper coated on the ZnS powder surface. Although the powder-type dc EL still has low luminous efficiency, the light output can be increased to a useful level by exciting the panel with voltage pulses of high peak power. The crosstalk effect in the display panel can also be suppressed, since the brightness is very nonlinear with respect to the applied voltage. The sealing of the panel with silicone oil is effective in lengthening the life of the panel. An experimental dc EL panel with a 13-in diagonal and 50 176 picture elements has been fabricated, capable of reproducing broadcast TV images. These images have a highlight brightness of 10 fL, a contrast ratio of 20:1, a limiting resolution of about 150 TV lines in both horizontal and vertical directions, and a gray-scale capability of 16 steps.
A precipitation method was found to be the most available forming process of the photoconductive (PC) layer for the X-ray image converting panel made of electroluminescent and photoconductive materials, To make a homogeneous PC-layer of 300-400 μm thickness with high reproducibility, the characteristics of the PC powder materials, resin binders and solvents were investigated and optimum conditions for the precipitation were established.The photo-sensitivity of the PC-layer increased by using a high speed stirring process, and a finer surface of the PC-layer was produced by controlling the difference of precipitation speeds between large and small PC-particles.As a result, the quality and resolution of the converted image were improved and the possible applying voltage of the panel increased. The improved panel showed a brightness of 12-15 ft-L, contrast of 1.5-1.8, X-ray sensitivity of 0.03-0.05 R/min and resolution of 0.25-0.3 mm by penetrameter, and suggested wider applications in the filed of X-ray non-destructive inspection.
A new photoconductive material suitable for an EL-PC type X-ray image converting panel was developed. The material was obtained by activating a mixture of CdSe, ZnS and ZnO with Cu as an activator and chlorine and bromine as co-activators. In this method, an addition of ZnS, which makes a solid-solution with CdSe, was effective to increase the threshold voltage of the material, that of ZnO, which suppresses excessive sintering at the firing step, was effective to decrease the particle size, and the optimum amounts of ZnS and ZnO were effective to improve the photosensitivity of the material. The X-ray image converting panel for which the material was applied had improved characteristics in brightness, contrast, threshold sensitivity and resolution.
