Characterization of structural and photoinduced defects in pure and doped lithium niobate

Abstract

In this work we report on the characterization of structural and defect-related properties of a series of lithium niobate single crystals with congruent and stoichiometric composition containing Fe and Mg dopant. In particular we investigate the role of UV and visible irradiation in the charge trapping mechanisms which control the photorefractive (PR) behaviour. Complementary techniques (Raman microscopy, Electron Paramagnetic Resonance, absorption measurements) were used to characterize the degree of crystal imperfections. This is the basic starting point for an exhaustive comprehension of PR behaviour, monitored observing photovoltaic current and photoconductivity.

EPR and Optical Absorption Investigations of Photochromic Effect in Nearly Stoichiometric LiNbO₃:Fe

“…[6], an x c value for our samples of about 49.8% has been evaluated from the ∆B values of the low field signal components, also in agreement with what previously obtained from the line-width of the Raman modes [7]. Optical absorption measurements evidenced an absorption band centered around 500 nm, typically observed for Fe 2+ ions [7,8]. About the reduced samples treated at 1073 K, no differences have been noticed, in both EPR and absorption spectra.…”

Influence of iron doping on spatial soliton formation and fixing in lithium niobate crystals

“…In this context, lithium niobate is known to be photorefractive in the visible spectral range: its photorefractive sensitivity (the maximum achievable refractive index change for a given light intensity) can be increased of many times by doping the material with metals possessing two states of valence, such as Fe 2+ /Fe 3+ since iron ions act as donors and traps of electrons [5,6], key parameters in the photo-excitation processes that drive photo-refractivity [7][8][9]. Lithium niobate technology has therefore the potential to include holographic stages into integrated optical circuits as already reported in bulk doped Fe:LiNbO 3 crystals by Ti in-diffusion [10]. Some data were reported also on the diffusion of Fe [11,12] and co-diffusion with Ti in LiNbO 3 crystals [13] with the purpose of realizing an Infrared integrated filter by means of a holographic grating.…”