Rare earth elements have been used as optical dopants in glasses for many years. Boro-silicate glass films doped with rare-earths were deposited on glass substrates by using a simple sol-gel method. To avoid the undesirable precipitation due to the different hydrolysis rates between silicon and boron alkoxides, two solutions were used for dip-coating separately. One solution consisted of silicon tetraethoxide, ethanol, water and terbium nitrate as the Tb dopant. Another consisted of triethyl borate. Layer-by-layer deposition was applied by dipping into solutions containing metal alkoxides in sequence. The fluorescence properties of Tb3+ were investigated for the boro-silicate samples in relation to the firing effect. As-deposited silicate and boro-silicate samples showed similar fluorescence spectra under UV excitation. After firings at about 800 degrees C, a remarkable increase of the Tb3+-ion fluorescence was observed for the boro-silicate samples, while the silicate sample showed a little increase in fluorescence intensity. These experimental results suggested the formation of boro- silicate network and the incorporation of Tb3+ into the boro-silicate matrix. The multilayer process was found useful to fabricate multi-component sol-gel films.
The high-voltage bulk photovoltaic effect in ferroelectrics was theoretically and experimentally studied focusing on the nonlinear dielectric response. The steady current in the absence of applied voltage, called `photocurrent', is considered as a result of photocarriers and the asymmetric electromotive force induced by near-ultraviolet radiation. A model accounting for the generation of electric field acting as an effective dc field for the photocarriers was explained in terms of the photoinduced nonlinear polarization and the Lorentz field in dielectrics. Experimental results on electric photoconductivity, photocurrent and photovoltage of a PLZT ceramic were analyzed by using exponential functions based on the model. An adjustable parameter was introduced in relation to the incoherence of the illuminating light as an electromagnetic wave. It was found that the exponential functions by the present model can give better fitting to the experimental data than that by a linear function previously used.
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