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Photoconductivity measurements are carried out in this work for single crystals of Tl 4 S 3 compound by using both pulsed excitation (a.c) and steady state (a.c) methods in order to elucidate the nature of photoconductivity (PC) in this compound. Results are reported in the temperature range from 77 to 300K, excitation intensity range from 1800 to 3300Lux, applied voltage range from 8 to 14V, and wavelength range from 840 to 1450nm. Both of the ac-photoconductivity (ac-PC) and the spectral distribution of the photocurrent are studied at different values of light intensity, applied voltage and temperature. Dependencies of carrier lifetime on light intensity, applied voltage and temperature are also investigated as results of the ac-PC measurements. By using the results of the dc-photoconductivity (dc-PC) measurements, the temperature dependence of the energy gap width is described.

Investigation of the electric properties of semi-conducting materials in an applied ac electric fields gives information about the nature of charge transport and localized states in the forbidden gap. Layered crystals usually contain structural defects, such as dislocations and vacancies that may form a high density of localized states near the Fermi level. So, the current study was carried out for insight into the dielectric Properties of Tl2S layered single crystals. These properties were studied using the ac measurements in the low temperatures ranging from 77 to 300 K. The real part of dielectric constant ε?, imaginary part of dielectric constant ε?, the dissipation factor tan δ and the alternating current conductivity σac were measured in an applied ac electric field of frequencies extending from 2.5 to 50 kHz. Based on the dependencies of these dielectric parameters on both the frequency and temperature, the dielectric properties of the crystals under investigation were elucidated and analyzed. The ac conductivity was found to obey the power law σac(ω) = Aωs with which the values of the exponent s were evaluated to be less than unity in the range 0.21 ≥ s ≥ 0.19. Furthermore, it was found that the temperature dependence of ac conductivity follows the Arrhenius relation via which the impact of temperature on the electrical processes in an applied ac electric field was illustrated and analyzed. The influences of temperature and frequency on both the exponent s and band gap were also discussed in this investigation

A glass system of 40P 2 O 5 -(21x) Na 2 O-38ZnO-x Co 3 O 4 -1CuO where (x = 1, 2, 3, 4 and 5) has been prepared by melt quenching technique. The density of the glasses was measured, and molar volume was calculated. The structure has been investigated using IR spectroscopy. The spectral analyses showed that the addition of Co 3 O 4 to P 2 O 5 glass is unequivocally influencing the shortrange order of the glassy matrix. The spectra also denote the formation of P-O-Co bonds in the glasses that replace P-O --Na ? bonds. The results are related to the dual role of cobalt ions as a glass former and modifier.

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