Electrical impedance measurements on a congruent LiNbO 3 single crystal were performed as a function of both temperature and frequency. The measurements were carried out in the directions along the cand a-axes of the crystal. The temperature and frequency dependence of various dielectric properties have been studied. The result has revealed two remarkable dynamic relaxations: dielectric dipolar relaxation and ionic conductivity relaxation. The dipolar relaxation peaks were found at frequencies around 4 × 10 6 and 2 × 10 6 Hz for the c-axis and a-axis, respectively, and they were only slightly temperature dependent. The ionic conductivity relaxation was found at the lower-frequency end but it was temperature dependent. The temperature dependence of the dc electrical conductivity follows the Arrhenius law. It corresponds to the longrange ionic motion of Li + ions which are thermally activated with activation energy of 0.90 and 0.87 eV along the cand a-axis directions, respectively. The dc conductivities measured along the cand a-axes are very close to each other, and the value increases from 1.7 × 10 −6 to 1.9 × 10 −3 −1 cm −1 as the temperature is raised from 300 to 700 • C. The sample crystal becomes an ionic conductor as the temperature is raised.
A new afterglow green phosphor of Zn2SiO4: Mn2+, Zr4+was prepared by high temperature solid-state method. Effects of various preparation techniques on the crystal characteristics, luminescent properties and afterglow performance have been investigated systematically. The phosphor powders were further investigated by photoluminescence excitation and emission spectra (PL) and brightness meter. The results showed that the PL of Zn2SiO4: Mn2+, Zr4+was observed in the green region due to transitions from the4T1g(G) to the5A1g(S) configuration of the Mn2+ions. This phosphor showed obvious long-lasting phosphorescence that could be clearly seen with naked eyes in a dark room for more than 2h after the irradiation source has been removed. The possible mechanism of this phosphor was also investigated based on the TL measurements.
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