Photorefraction of molybdenum-doped lithium niobate crystals

Unveiling the Defect Structure of Lithium Niobate with Nuclear Methods

X-ray and neutron diffraction studies succeeded in the 1960s to determine the principal structural properties of congruent lithium niobate. However, the nature of the intrinsic defects related to the non-stoichiometry of this material remained an object of controversial discussion. In addition, the incorporation mechanism for dopants in the crystal lattice, showing a solubility range from about 0.1 mol% for rare earths to 9 mol% for some elements (e.g., Ti and Mg), stayed unresolved. Various different models for the formation of these defect structures were developed and required experimental verification. In this paper, we review the outstanding role of nuclear physics based methods in the process of unveiling the kind of intrinsic defects formed in congruent lithium niobate and the rules governing the incorporation of dopants. Complementary results in the isostructural compound lithium tantalate are reviewed for the case of the ferroelectric-paraelectric phase transition. We focus especially on the use of ion beam analysis under channeling conditions for the direct determination of dopant lattice sites and intrinsic defects and on Perturbed Angular Correlation measurements probing the local environment of dopants in the host lattice yielding independent and complementary information.

Lithium Niobate Single Crystals and Powders Reviewed—Part II

A review on lithium niobate single crystals and polycrystals has been prepared. Both the classical and recent literature on this topic is revisited. It is composed of two parts with several sections. The current part discusses the available defect models (intrinsic), the trends found in ion-doped crystals and polycrystals (extrinsic defects), the fundamentals on dilute magnetic oxides, and their connection to ferromagnetic behavior in lithium niobate.

Interaction between Mo and intrinsic or extrinsic defects of Mo doped LiNbO3 from first-principles calculations

Lithium niobate (LiNbO₃, LN) plays an important role in holographic storage, and molybdenum doped LiNbO₃ (LN:Mo) is an excellent candidate for holographic data storage. In this paper, the basic features of Mo doped LiNbO₃, such as the site preference, electronic structure, and the lattice distortions have been explored from first-principles calculations. Mo substituting Nb with its highest charge state +6 is found to be the most stable point defect form. The energy levels formed by Mo with different charge states are distributed in the band gap, which are responsible for the absorption in the visible region. The transition of Mo in different charge states implies molybdenum can serve as a photorefractive center in LN:Mo. In addition, the interactions between Mo and intrinsic or extrinsic point defects are also investigated in this work. Intrinsic defects [Formula: see text] could cause the movement of the [Formula: see text] energy levels. The exploration of Mo, Mg co-doped LiNbO₃ reveals that although Mg ion could not shift the energy level of Mo, it can change the distribution of electrons in Mo and Mg co-doped LN (LN:Mo,Mg) which help with the photorefractive phenomenon.

Computer Simulation of the Incorporation of V2+, V3+, V4+, V5+ and Mo3+, Mo4+, Mo5+, Mo6+ Dopants in LiNbO3

The doping of LiNbO3 with V2+, V3+, V4+ and V5+ as well as Mo3+, Mo4+, Mo5+ and Mo6+ ions is of interest in enhancing its photorefractive properties. In this paper, possible incorporation mechanisms for these ions in LiNbO3 are modelled, using a new set of interaction potentials fitted to the oxides VO, V2O3, VO2, V2O5 and to LiMoO2, Li2MoO3, LiMoO3, Li2MoO4.

The Photorefractive Response of Zn and Mo Codoped LiNbO3 in the Visible Region

We mainly investigated the effect of the valence state of photorefractive resistant elements on the photorefractive properties of codoped crystals, taking the Zn and Mo codoped LiNbO3 (LN:Mo,Zn) crystal as an example. Especially, the response time and photorefractive sensitivity of 7.2 mol% Zn and 0.5 mol% Mo codoped with LiNbO3 (LN:Mo,Zn7.2) crystal are 0.65 s and 4.35 cm/J at 442 nm, respectively. The photorefractive properties of the LN:Mo,Zn crystal are similar to the Mg and Mo codoped LiNbO3 crystal, which are better than the Zr and Mo codoped LiNbO3 crystal. The results show that the valence state of photorefractive resistant ions is an important factor for the photorefractive properties of codoped crystals and that the LN:Mo,Zn7.2 crystal is another potential material with fast response to holographic storage.

Photorefractive Properties of Molybdenum and Hafnium Co-Doped LiNbO3 Crystals

A series of LiNbO3: Mo, Hf crystals with 0.5 mol % fixed MoO3 and various HfO2 concentrations (0.0, 2.0, and 3.5 mol %) were grown by the Czochralski technique. The photorefractive properties of the LiNbO3: Mo, Hf crystals were investigated by two-wave coupling measurements and the beam distortion method was employed to obtain the optical damage resistance ability. The UV-visible and OH− absorption spectra were also studied. The experimental results imply that the photorefractive properties of LiNbO3: Mo crystals at laser wavelengths of 532, 488, and 442 nm can be greatly enhanced by doping HfO2 over the threshold concentration. At 442 nm especially, the response time of LN: Mo, Hf3.5 can be shortened to 0.9 s with a diffraction efficiency of 46.07% and a photorefractive sensitivity reaching 6.28 cm/J. Besides this, the optical damage resistance at 532 nm is 3 orders of magnitude higher than that of the mono-doped LiNbO3: Mo crystal, which is beneficial for applying it in the field of high-intensity lasers.

The simultaneous enhancement of photorefraction and optical damage resistance in MgO and Bi2O3 co-doped LiNbO3 crystals

For a long time that optical damage was renamed as photorefraction, here we find that the optical damage resistance and photorefraction can be simultaneously enhanced in MgO and Bi2O3 co-doped LiNbO3 (LN:Bi,Mg). The photorefractive response time of LN:Bi,Mg was shortened to 170 ms while the photorefractive sensitivity reached up to 21 cm(2)/J. Meanwhile, LN:Bi,Mg crystals could withstand a light intensity higher than 10(6)  W/cm(2) without apparent optical damage. Our experimental results indicate that photorefraction doesn't equal to optical damage. The underground mechanism was analyzed and attributed to that diffusion dominates the transport process of charge carriers, that is to say photorefraction causes only slight optical damage under diffusion mechanism, which is very important for the practical applications of photorefractive crystals, such as in holographic storage, integrated optics and 3D display.

Effect of electrostatic and size on dopant occupancy in lithium niobate single crystal

We proposed a simple and an effective method to predict the site occupancy and threshold concentration of metal ions in lithium niobate (LiNbO3, LN) single crystal. The ionic energy parameter E(i), defined by the ionic electronegativity and ionic radius, was proposed to describe the electrostatic and size effects of cations on the structural stability of LN. The dopant location can be easily identified by comparing the E(i) deviation of dopant from those of host cations Li(+) and Nb(5+), and the dopant prefers to occupy the lattice site with the smaller deviation of E(i). Our calculated occupancies agree well with those experimental results, which demonstrate the predictive power of our present method. We in this work predicted the preferred occupancies of 60 metal ions in LN single crystal. Further, the threshold concentrations of some frequently used dopants were calculated on the basis of the assumption that all doped LN crystals can endure the same variation of E(i).

Fast UV-Vis photorefractive response of Zr and Mg codoped LiNbO3:Mo

A series of LN:Mo,Zr and LN:Mo,Mg crystals with different doping concentrations were grown and their holographic properties were investigated from UV to the visible range. Each crystal allows for holographic storage from UV to the visible as LN:Mo. When the concentration of MgO is enhanced to 6.5 mol%, the response time can be dramatically shortened to 0.22 s, 0.33 s, 0.37 s and 1.2 s for 351, 488, 532, and 671 nm laser, respectively. The results show that LN:Mo,Mg is a promising candidate for all-color holographic volume storage with fast response.

Recent Advances in the Photorefraction of Doped Lithium Niobate Crystals

The recent advances in the photorefraction of doped lithium niobate crystals are reviewed. Materials have always been the main obstacle for commercial applications of photorefractive holographic storage. Though iron-doped LiNbO₃ is the mainstay of holographic data storage efforts, several shortcomings, especially the low response speed, impede it from becoming a commercial recording medium. This paper reviews the photorefractive characteristics of different dopants, especially tetravalent ions, doped and co-doped LiNbO₃ crystals, including Hf, Zr and Sn monodoped LiNbO₃, Hf and Fe, Zr and Fe doubly doped LiNbO₃, Zr, Fe and Mn, Zr, Cu and Ce triply doped LiNbO₃, Ru doped LiNbO₃, and V and Mo monodoped LiNbO₃. Among them, Zr, Fe and Mn triply doped LiNbO₃ shows excellent nonvolatile holographic storage properties, and V and Mo monodoped LiNbO₃ has fast response and multi-wavelength storage characteristics.