Fluorescence characteristics of gallium nitride powder samples prepared in our laboratory were examined. The samples processed at 1100 °C showed band-edge emission and yellow luminescence, but the samples processed at 900 or 1000 °C showed no significant fluorescence. From the results of XRD analysis, it was confirmed that all these samples had wurtzite gallium nitride structure, and the samples processed at 900 or 1000 °C showed the very low crystallinity. It was suggested that a lot of defects were present in the crystals of these powder samples with low crystallinity, so that the recombination of excited electrons and holes was promoted to show no significant fluorescence emission. In addi- tion, the sample processed with coexistence of activated carbon at a high ratio showed blue light emission around 425 nm, and it was con- cluded that a certain amount of carbon was taken into the crystal lattice.

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The system used to analyze the process of the formation of latent image specks (LISs) in silver-salt photographic materials due to radiation exposure to obtain the dispersion index, which is the number of LISs in a silver halide grain formed by one impact of high-energy particle, was improved. By using the electron beam from a transmission electron microscope, electrons of uniform energy could be produced for irra- diation purposes. The number of electrons impacting a single silver halide grain along with the energy of each electron was controlled by varying the current density and the applied voltage. A new analysis method which included the probability that LIS may not be formed de- spite an impact of high-energy particle was proposed. The number of LISs was counted by the arrested development method. The probability and the dispersion index were estimated at approximately 0.5 and 1, respectively, for an unsensitized emulsion with cubic grains. This method will be useful in the design of new nuclear emulsion plates.

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