B. M. Jin

Possible trends for the growth of low scattering Nd:YVO4 laser crystals; phase relations — growth techniques☆

Abstract The Nd:YVO 4 single crystal is one of the most promising laser hosts for micro and diode-pumped solid state lasers due to its outstanding laser characteristics. However, the growth difficulties encountered can significantly restrain its widespread high-tech applications. The inclusions which are mainly submicron size precipitates, and the color center problems commonly originate from the defects of valency states. The presence of non-pentavalent vanadium ions in the V 2 O 5 starting material, the related valency defects in the YVO 4 compound created by the reaction process, and the in congruent vaporization of vanadium oxides together with YVO 4 melt will primarily determine the congruency as a typical off-stoichiometric effect. This work concludes that the simple Czochralski (CZ) growth technique cannot produce scatterin-free and stoichiometric YVO 4 crystals, nevertheless the top-seeded solution growth (TSSG) and liquid phase epitaxial (LPE) techniques provide possible alternatives for better quality crystal production. Several specific aspects of the phase relations of YVO 4 crystals prepared by CZ, TSSG and LPE techniques are surveyed in this paper.

Micro-probe Raman spectroscopy for detection of inhomogeneities in YVO4 single crystals

Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1 was measured for full width at half‐maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1 frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm−1 frequencies in all CZ grown samples. The above detected changes in Y–V–O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO4 specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO4 single crystals than previously available.Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1 was measured for full width at half‐maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1 frequencies. In addition, nonassigned low intensity extra Raman pe...

Characteristics of MgO-doped LiNbO3 crystals

Abstract Congruent MgO:LiNbO 3 (MLN) single crystals doped with 0, 2.5, 5.0, 7.5 and 10.0 mol% of MgO contents were grown by the Czochralski method. The grown crystals were water clear without any precipitation. The density and Curie temperature ( T C ) for MLN crystals were measured. The Curie temperature increased first with the MgO concentration and decreased again when the concentration of MgO went beyond the threshold limit ([Mg] C , 5.0–7.5 mol%). We also measured optical absorption edge and IR absorption spectra at room temperature for MLN crystals. The threshold concentration of nearly 6.0 mol% was estimated. The IR absorption peak appeared at 3470 cm −1 in 0–5.0 mol% and at 3534 cm −1 in 7.5–10.0 mol%; the peak shifted about 60 cm −1 toward the shorter wavelength side.

Raman study of oxygen deficient YVO4 single crystals

Oxygen deficiency which is an inherent problem in melt grown YVO{sub 4} single crystals was investigated by Micro-Probe Raman Spectroscopy (MPRS). External vibrational modes at 157 cm{sup {minus}1}, 162 cm{sup {minus}1} and selected internal vibrational modes at 379 cm{sup {minus}1}, 840 cm{sup {minus}1} of full Raman spectra were compared with different YVO{sub 4} crystals grown by the Czochralski (CZ) technique both with and without annealing in an O{sub 2} atmosphere as well as by top seeded solution growth technique (TSSG) in directly produced oxygen deficiency-free form. Special differences of above mentioned frequencies and over 1,000 cm{sup {minus}1} were observed in the Raman spectra, which could prove that the growth technologies generated different rates of oxygen deficiency in addition to critical intrinsic segregation effects in YVO{sub 4} which significantly determine the crystal quality.

UV absorption edge position for characterization of YVO4 crystals growth by Czochralski and TSSG techniques

Abstract The UV absorption edge of YVO 4 crystal with a slight yttrium excess grown by Czochralski (CZ) technique, after annealing in O 2 atmosphere, was compared with oxygen deficiency-free YVO 4 crystals grown by the top seeded solution growth (TSSG) technique. The measurements show that the TSSG crystal has higher transparency in near-UV than the CZ sample, demonstrating a better near-stoichiometric composition in the TSSG-YVO 4 single crystal.

Raman spectroscopy of sol-gel derived BaMg13Ta23 perovskites

Barium magnesium tantalate (BMT) perovskite was prepared from organic precursors including Ba metal, Mg (OC 2 H 5 ) 5 and Ta(OC 2 H 5 ) 5 . Crystallization and phase formation were studied for the sol-gel derived BMT powders. Microstructure of BMT shows particle sizes less than 0.1 μm. Raman spectroscopy was done to study the modes of vibration in the BMT ceramics.

Modification of UV-VIS optical absorption properties caused by MgO incorporation in MgO-doped LiNbO3 crystals

MgO-doped LiNbO3 single crystals were investigated in the UV-VIS range to study the effect of MgO in the LiNbO3 host. Congruent LiNbO3 has an optical absorption edge of 3.75 eV. Analysis of the absorption edge gave an estimate of the indirect band gap for MgO-LiNbO3 solid solutions. The band gap shows an MgO threshold effect in the absorption coefficient. An additional indirect transition at 2.2–2.5 eV was revealed when MgO was incorporated into the lithium niobate structure. This indirect transition also has a MgO threshold effect around 5 mol% MgO.

Micro-probe Raman spectroscopy of YVO4 single crystals grown by different growth techniques for investigation of micro-inhomogeneities

Abstract Micro-probe Raman spectroscopy was utilized for the investigation of three YVO 4 crystals grown by different growth techniques, rapid Czochralski growth (CZ1), top seeded solution growth (TSSG) and automatic diameter controlled Czochralski growth (CZ2). All of the Raman active modes below 1000 cm −1 are stable and homogeneous throughout the crystals. There exist distinctive differences between the differently grown crystals above 1000 cm −1 .

Growth and characterization of l-valine doped tgs single crystals

Dielectric and pyroelectric properties were investigated for L-valine (LV) doped triglycine sulphate (LVTGS) single crystals grown by a slow cooling technique from LV (10 mol% and 20 mol%) doped TGS aqueous solution. Extremely high permittivity maxima (e.g. Kmax = 376,531 at 100 Hz) were observed at the secondary phase transition temperature (Tc = 49°C), presumably related to specific hydrogen bonds created by the aliphatic LV amino acid dopant. In spite of its low incorporation, the L-valine dopant induces high pyroelectric coefficients (p = 1.671 μC/cm2 K at Tc) and generates a 0.2 kV/cm internal bias field in the mechanically stable 20% LVTGS single crystal. At both room and Tc temperatures the dielectric constants decrease, the pyroelectric properties increase with increasing LV concentration (K = 45.5, p = 85 nC/cm2K at 25°C in 20% LVTGS crystal).

Frequency dependence of the dielectric properties in MgO:LiNbO3 crystals

Abstract MgO-doped congruent composition LiNbO3 crystals were grown by the Czochralski method. All MgO:LiNbO3 melts have a higher melting temperature than that of a pure one. Frequency dependence dielectric spectra were measured to study the relaxation and conduction mechanism of these crystals. Strong, low frequency dispersion indicated that the main conduction of MgO-doped LiNbO3 is the hopping charge carrier which may be caused by the defects or Mg-ions. Impedance spectra measurements show that this system does not satisfy a Debye but Jonschers “Universal Law”