Research On Electrical Conductivity Of Lithium Niobate Under Laser Exciting

Lithium Niobate (LiNbO3:LN for short) is one of the most important multifunctional artificial crystals. It possesses excellent nonlinear-optics, electro-optics, acousto-optics, photo-refractive properties. It also has good chemical stability and mechanical stability. So it widely used in electro-optical, nonlinear optical applications of all kinds. Precise knowledge of the light-induced (such as light-induced absorption, light-induced conductivity, etc.) charge transport governed by defect centers of LN is an indispensable prerequisite for any of these applications.In this paper, four iron doped LN crystals (with different Fe ion concentration) and two kinds of pure LN crystals (with different Li/Nb) were measured by the method of voltammetric measurement. We get the experiment results as follows:1. When uniform illumination reached the steady-state, the currents flowing through samples appear to fixedness. In the same voltage, along with the increase of iron ion concentration, crystals conductivity will also corresponding increase.2. For Fe doped LN crystals, the conductivities increases with the increased voltage, and the higher iron ion concentration, the conductivity increases faster.3. When the laser is closed, crystals'conductivities decrease with time. For the same crystals, the higher voltage is applied, the faster of conductivity decay; in the same voltage, if the crystal holds the higher iron ion concentration, it's conductivity has the bigger relative variation, and the relaxation times to the steady-state are also longer.4. For pure LN crystals of different component, deviating from the stoichiometric ratio will make the crystals'dark conductivities and light conductivities change bigger, the relaxation time will also corresponding smaller.Combining the doubly center model theoretical and experimental results, we obtained the corresponding parameters. We think, the LN crystals have weak lasting photoconductive effect, the illumination, external electric fields and the different mixed iron concentration of crystals are the important reasons to caused the conductance changes.