Heavy metal selenides have shown very good properties including wavelength conversion in MWIR and LWIR regions, acousto-optic and great potential for radiation detection. We have extensively studied thallium-based compounds for variety of applications. Studies were performed for crystal growth, fabricability and radiation detection characteristics of ternary congruent compounds of thallium mercury iodide system from the melt by Bridgman method. The congruency and phase transition was studied by DTA. Material melts congruently between 300-400 0C and do not show any other phases between room temperature and melting point. Crystal slabs were fabricated as bulk detector to demonstrate good characteristics for detectivity of X-ray and gamma-rays. Effect of impurities on performance were evaluated by using source materials of different purity for synthesis. Crystals with high purity source materials and mixed by vibrating method were determined for resistivity in range of 1012ohm-cm.
A great deal of research has been performed on refractive index n and extinction coefficient k due to varieties of applications in optical industries. The dispersion equation is described for the photons of varying energies and their interactions with materials since there is a strong correlation of n and k with wavelength. Measurements based on reflectance can be expensive and are very difficult due to compositional variations. We present a low-cost reflectance probe fiber optics designed in-house to determine the absorption coefficients and refractive index of solids. The solutions using a modified Beer-Lamberts Law and merging the concentration and extinction coefficient terms into an absorption coefficient, α, can be given by the equation I = I0 exp (-α* d) where I is the transmitted intensity, I0 is incident intensity and d is the thickness. We have experimented with several semiconductor compounds for this study.
Polarity is very important in developing materials with colossal dielectric. To meet the demands for the tunable devices and high dielectric parallel plate capacitors, several perovskites such as CaCu3Ti4O12 (CCTO), La2/3Cu3Ti4O12 (LCTO) Pr2/3Cu3Ti4 O12 (PCTO) and several other materials of this class have been studied all over the world. Detailed studies showed that results vary a lot based on processing methods, such as powder vs. multi crystals and single crystals. In spite of great progress in processing, low resistivity and process driven variables in properties remain a big hurdle for its applications as a dielectric capacitor. We observed that dielectric values are significantly changed when these materials are exposed to chemicals and biological agents. We used parallel plate capacitor design for making chemical and biological sensors from CCTO member of this group. The data indicated huge difference in the dielectric and resistivity of the exposed samples.
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