Optical properties and structure particularities of LiNbO3 crystals grown from a boron-doped melt

A series of LiNbO3:B crystals was grown from the melt doped by boron. It is shown that LiNbO3:B crystals possess an increased resistance to optical damage. We have found changes according to Raman spectra confirming the ordering of Li+, Nb5+ cations and vacancies along the polar axis. The chemical interactions were studied in the system Li2O–B2O3–Nb2O5. Boron cations are unable to incorporate into a cation sublattice of LiNbO3, but they change the physic-chemical structure of a melt. It contributes to an increased structure and optical uniformity of LiNbO3:B.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Growing, Structure and Optical Properties of LiNbO3:B Crystals, a Material for Laser Radiation Transformation

Physical and chemical properties have been studied in lithium niobate (LiNbO3, LN) crystals grown by Czochralski from a boron doped melt. Optical uniformity and optical damage resistance of LiNbO3:B crystals have been compared with control crystals of nominally pure congruent (CLN) and near-stoichiometric (NSLN K2O) composition. LiNbO3:B crystals structure has been studied. Studied LiNbO3:B crystals have been grown from differently synthesized charges. The charges have been synthesized from a mixture Nb2O5:B-Li2CO3 using homogeneously doped Nb2O5:B precursor (sample 1, (B) = 0.0034 wt% in the charge) and by a direct solid phase synthesis from Nb2O5-Li2CO3-H3BO3 mixture (sample 2, (B) = 0.0079 wt% in the charge). Only traces of boron (10−5–10−4 wt%) have been detected in the samples. We have established that concentration of anti-site defects NbLi is lower in both LiNbO3:B than in CLN crystals. XRD analysis has confirmed that B3+ cations localize in faces of tetrahedral voids O4 of LN structure. The voids act as buffers at the anion sublattice distortion. Sample 1 has been shown to have a structure closer to NSLN K2O crystal than sample 2. We have also shown that the chemical purity of LN crystal increases compared to the melt purity because boron creates strong compounds with impurities in the melt system Li2O-Nb2O5-B2O3. Metals impurities thus stay in the melt and do not transfer to the crystal

Raman Scattering in a Double-Doped Single Crystal LiTaO3:Cr(0.2):Nd(0.45 wt%)

The Raman spectra of a lithium tantalate crystal doubly doped with chromium and neodymium LiTaO3:Cr(0.2):Nd(0.45 wt%) have been studied in this paper. Raman spectra of the first and second orders have been found to be located against the background of a luminescent halo with a maximum at ≈1250 cm−1. Several Raman bands have been detected in the frequency range of 900–2000 cm−1. Their frequencies were 940, 1034, 1113, 1171, 1250, 1343, 1428, 1491, 1582, 1735, 1838, and 1925 cm−1. These bands correspond to overtone processes. We have determined that the frequencies of 1838 and 1925 cm−1 bands are significantly higher than the exact value of the overtone frequency corresponding to the fundamental mode 4A1(z)LO (864 cm−1)

NMR Spectra Particularities in LiNbO3 Crystals with a Near-Stoichiometric Composition

The paper studies LiNbO3 (LN) crystals with a near-stoichiometric composition (NSLN). The study establishes the possibility of different physical methods to reveal NSLN crystals’ exact composition. The main goal was to establish how precisely these methods can reveal a NSLN composition, including a defective structure. This structure determines properties that are important for the application of the crystals. Two NSLN crystals with a different Li/Nb ratio have been studied by IR and NMR spectroscopy. NSLN crystals have been grown from a congruent melt with different K2O flux contents (5.0 and 5.5 wt%). The data on NSLN have been compared with the data on congruent (CLN) crystals. CLN are the most widely used LN crystals. The study has established that analysis of the IR spectra can determine the Li/Nb ratio within [Li2O] = 48.6 – 50.0 mol% range, while the 93Nb NMR spectra has a wider range of sensibility. LN crystals’ stoichiometry or the Li/Nb ratio determine the concentration of antisite defects NbLi. Niobium substitutes lithium in its octahedron. Such defects appear up to [Li2O] = 49.9 mol%. Thus, the study shows that IR and NMR spectroscopy are sensitive methods that can complement each other when determining the precise LN composition (Li/Nb ratio) and the presence of intrinsic defects in the crystals

Second-Order Raman Scattering in Ferroelectric Ceramic Solid Solutions LiNb_xTa_1−xO₃

In the second-order Raman spectra of ceramic solid solutions, LiNbxTa1−xO3 weak overtone bands of fully symmetric fundamental polar excitations were observed for the first time. The frequencies of the two bands exceeded the value of the overtone frequency corresponding to the fully symmetrical vibration 4A1(z). The possibility of the existence of phonon bound states of the antipolar type in the vibrational spectrum of LiNbxTa1−xO3 ceramics is predicted

Investigation of the Structural Perfection of a LiNbO₃:Gd³⁺(0.003):Mg²⁺(0.65 wt.%) Double-Doped Single Crystal Using the Raman Spectra Excited by Laser Lines in the Visible (532 nm) and Near-IR (785 nm) Regions

A compositionally homogeneous nonlinear optical single crystal of double-doped LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%) was obtained. Fine features of the LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%) crystal structure were studied from the Raman spectra of the first and second orders upon excitation by laser lines in the visible (532 nm) and near-IR (785 nm) regions. When the Raman spectrum was excited by a 785 nm laser line in the frequency range of 1000–2000 cm−1 for the first time, a number of low-intensity lines in the range of 900–2000 cm−1, corresponding to the second-order Raman spectrum, were discovered. The same lines also appear in the spectrum upon excitation by a laser line with a wavelength of 532 nm, but their intensities are significantly (by an order of magnitude or more) lower. It is shown that in the structure of the double-doped LiNbO3:Gd3+(0.003):Mg2+(0.65 wt.%), the crystal oxygen-octahedral clusters MeO6 (Me–Li, Nb, Gd, Mg) are slightly distorted, and in addition, the value R = [Li]/[Nb] ≈ 1 is close to that for a nominally pure stoichiometric crystal

Radiation Modification of Optical Characteristics of LiNbO3:Zn and LiNbO3:Mg Crystals

The modification of the optical characteristics of LiNbO3:Zn and LiNbO3:Mg crystals grown by the Czochralski method was investigated using β and γ radiation. The photorefractive effect was found to be inhibited by ionizing radiation in the LiNbO3:Zn ([ZnO] ≈ 2.1 mol%) crystal, which belonged to a below-threshold concentration range. The inhibition was attributed to a stepwise radiation annealing of charged defects. Ionizing radiation increased the general optical uniformity of above-threshold crystals LiNbO3:Zn ([ZnO] ≈ 5.9 mol%) and LiNbO3:Mg([MgO] ≈ 5.6 mol%). In addition, we determined that radiation annealing substantially influenced photorefraction dynamics in lightly doped LiNbO3:Zn ([ZnO] ≈ 0.1 mol%) crystals, which widens their application areas

Some Optical Properties of LiNbO₃:Gd³⁺(0.003):Mg²⁺(0.65 wt %) Single Crystal: A Promising Material for Laser Radiation Conversion

A nonlinear optical double-doped single-crystal LiNbO3:Gd:Mg (Gd concentration is 0.003, Mg—0.65 wt % in the crystal) has been researched by several optical methods: laser conoscopy, photoinduced light scattering (PILS), optical spectroscopy, and Raman scattering. The crystal has been shown to have no photorefraction effect and a high optical uniformity. Fine features of the crystal structure have been studied via Raman spectra. Spectra have been registered in the first and second orders, they have been excited by visible (532 nm) and near-IR (785 nm) lasers. Registered Raman spectra have the fundamental vibrations of the crystal lattice of the A1(TO,LO)- and E(TO,LO)-type symmetry located in the range of 150–900 cm−1. A number of low-intensity Raman bands in the 900–2000 cm−1 region have been determined to correspond to the second-order Raman spectrum. These bands are polarized and appear only in certain polarization-scattering geometries. They appear in the spectrum excited by visible radiation, but their number and intensity are much lower than those excited by near-IR lasers. Oxygen-octahedral MeO6 clusters in our case can contain Li, Nb, Gd, or Mg in the Me site. The clusters in the LiNbO3:Gd:Mg crystal structure are slightly distorted compared with similar clusters in the nominally pure LiNbO3 crystal. It has been established that the value R = [Li]/[Nb] in the studied crystal is ≈ 1. Such a ratio usually characterizes a nominally pure stoichiometric crystal

Synthesis and Optical Characteristics of Gd_0.96Eu_0.01Sm_0.01Tb_0.01Er_0.01Nb_0.9Ta_0.1O₄ Ceramic Solid Solutions Prepared under Different Temperature Conditions

Fine powders of mixed gadolinium tantalum niobates doped with Eu, Sm, Tb, and Er were synthesized. Ceramic samples of polycomponent solid solutions of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 were obtained from synthesized powders using conventional sintering technology. The phase composition and phase structure characteristics of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic phases were determined by XRD. The effect of ceramic sintering temperature on the physical characteristics of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 solid solutions is shown. The morphological features of the microstructure of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics were studied in relation to its mechanical characteristics. At the same time, the strength characteristics (Young’s modulus, microhardness) and the critical stress intensity factor for mode I KIC were evaluated for the first time for the synthesized compounds. Photoluminescence and cathodoluminescence were studied in the visible region. The study confirms the potential application of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic solid solutions as scintillators and radioluminescent light sources

Synthesis and Optical Characteristics of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 Ceramic Solid Solutions Prepared under Different Temperature Conditions

Fine powders of mixed gadolinium tantalum niobates doped with Eu, Sm, Tb, and Er were synthesized. Ceramic samples of polycomponent solid solutions of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 were obtained from synthesized powders using conventional sintering technology. The phase composition and phase structure characteristics of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic phases were determined by XRD. The effect of ceramic sintering temperature on the physical characteristics of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 solid solutions is shown. The morphological features of the microstructure of the Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramics were studied in relation to its mechanical characteristics. At the same time, the strength characteristics (Young’s modulus, microhardness) and the critical stress intensity factor for mode I KIC were evaluated for the first time for the synthesized compounds. Photoluminescence and cathodoluminescence were studied in the visible region. The study confirms the potential application of Gd0.96Eu0.01Sm0.01Tb0.01Er0.01Nb0.9Ta0.1O4 ceramic solid solutions as scintillators and radioluminescent light sources