Characteristic features of ultraviolet photorefraction in iron-dopedα−LiIO3at low temperatures

Abstract

The temperature dependence of ultraviolet photorefraction of iron-doped ␣-LiIO 3 crystals is studied. Within the temperature range of 120-220 K diffraction efficiency and two-wave mixing gain increase dramatically with decreasing temperature and become as high as 36% and 3.1 cm Ϫ1 , respectively, below 120 K. The results of holographic recording experiments are compared with measurements of the dielectric susceptance, electric conductivity, and absorption of acoustic waves to establish a relationship between the change in photorefraction and the temperature dependence of the dielectric and ultrasonic behavior. Iron doping of ␣-LiIO 3 enhances the photorefraction considerably. ͓S0163-1829͑98͒05615-X͔

Low-Frequency Relaxation Phenomena in α-LiIO3: The Nature and Role of Defects

“…For example, in the case of Fe 3+ (ionic radiusE0.55 ( A) doped acid-type crystals Xu et al (13) determined, in the range 193-300 K, an activation energy of 0.2670.02 eV with which we obtain a transition temperature of T=200728 K consistent with Fig. 3.…”

“…Below RT, the maximum absorption was found to greatly depend on the growth conditions (6,13). This latter fact, usually attributed to an intrinsic cooperative motion of Li + ions, seems to be governed, more likely, by the behavior of extrinsic defects.…”

“…Lowering temperature changes the long-range redistribution of vacancies to a bulk one and then, prevents the formation of space charges partially responsible for the above phenomena (33,34). According to the sample composition, this frozen LT redistribution could also account for the appearance of a strong photorefractive effect below 200-220 K where small displacements of vacancies stop screening the photoinduced electronic charge-density grating during two-wave mixing experiments (12,13).…”

Growth and electrical properties of Mg:α-LiIO3 crystal

“…Because the optical properties of a-LiIO 3 crystals are strongly related to the quasi-one-dimensional ionic conduction [2,8,9], the influence of defects and growth conditions upon the ionic conductivity of a-LiIO 3 crystals has attracted more attention [10][11][12][13]. The strong increase of the ultraviolet photorefractive effect in iron-doped a-LiIO 3 below 200 K has been associated with the freezing of the ionic conduction [14,15]. In addition, some new applications in the fields of optical data storage and waveguides have been investigated by doping transition metals [14][15][16][17] and proton exchange [18,19] in a-LiIO 3 crystals.…”

The photo-neutronrefractive effect

“…Promising material for this type of effect is LiIO 3 , which is known as a quasi onedimensional ionic conductor at ambient temperatures. Moreover, photorefractive properties have been proven to exist at temperatures below 180 K [154,155,156]. As the neutronrefractive-index changes are proportional to the concentration modulation ∆c ion of the specific ion, we expect that at lower temperatures the ionic grating must be very efficient in diffracting neutrons.…”