Comparative Study of Composition Dependences of Photorefractive and Related Effects in LiNbO₃and LiTaO₃Crystals

Abstract

The results of a comparative study of composition dependences of the light-induced refractive index change, photorefractive sensitivity, polaron luminescence, and intrinsic optical absorption in nominally pure LiNbO 3 and LiTaO 3 crystals are reported. Our investigation demonstrates that the particular light-induced defects traced by the photoluminescence are secondary photorefractive centers itself. The experimental results obtained are well described by light-induced dissociation of bipolarons into small polarons that are unstable at room temperature.

Polaron luminescence in iron-doped lithium niobate

“…On another hand, the spectral characteristics of the PL band, similar to the light-induced absorption band of bound polarons but slightly shifted to longer wavelengths, do not leave any ambiguity on the nature of the intrinsic defect involved. The fact that this PL band vanishes in stoichiometric LN [15] and in compensated LN:Mg 6% mol [14] definitely confirms that the niobium antisite defect Nb Li , or otherwise a complex defect including Nb Li ,is responsible for the PL process.…”

Recent Advances in the Photorefraction of Doped Lithium Niobate Crystals

“…Bipolarons and small polarons can act as photorefractive centers and transform into each other by illumination with suitable light or with heat treatment [ 51 , 52 ]. And, in the visible region, the photorefractive centers of PLN were proven to be bipolarons and small polarons [ 53 ]. Hesselink et al have utilized these bipolarons and small polarons to achieve nonvolatile holographic storage in PLN [ 54 ].…”

Structure and Luminescent Properties of Double‐Doped LiNbO3:Zn:Mg Crystals

“…The luminescence band at ≈1.50 eV, being the most sensitive to changes in the composition of the LiNbO 3 crystal, is due to the Nb Li small‐radius polaron. [ 20,22,36,42,43 ] With the increase in zinc concentration in the studied samples, there were less Nb Li defects. This was accompanied by the increase in luminescence intensity at ≈1.50 eV.…”

“…The low‐intensity maxima in Figure 2b (marked with *) were associated with radiative transitions of impurities with the unfilled 3d orbitals, whose concentration in the crystal was at the level of trace amounts (10 −4 wt%). [ 20,40–42 ]…”

“…Previously, polaron luminescence was studied only in LiNbO 3 crystals of nominally pure composition and some LiNbO 3 crystals doped with Fe and Ti. [ 20–22 ]…”