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Abstract: We report that potassium meta-phosphate (KPO3) is an adequate solvent for high-temperature fluxing salt of LiNbO3 crystal. As the KPO3 is used as the solvent, the solubility of LiNbO3 is as high as 3 g g−1 at 1050 °C. The dissolving is fast. Neither solute nor solvent evaporates from the melt during the dissolving procedure. A clear solution is obtained and verified valid for crystal composition analysis using chemical method of inductively coupled plasma atomic emission spectroscopy. To help for understanding the dissolving mechanism, the obtained fluxing melt product was further characterized using X-ray diffraction, nuclear magnetic resonance and Raman scattering spectroscopy. The results show that the melt is amorphous. The P ion in the melt is in the form of low condensation and the Nb ion is likely in the form of Lindqvist ion. Finally, the dissolving mechanism is discussed. [Copyright &y& Elsevier]

Abstract: A thermodynamic study on Li-poor vapor transport equilibration (VTE) in MgO-doped LiNbO3 crystal was carried out. A thorough thermodynamic VTE model is established that considers all of possible factors including the depth relative to crystal surface, VTE temperature and time. To solve the model, the composition on crystal surface was studied as a function of VTE temperature and time. To achieve that, a number of Li-deficient MgO(5 mol% in melt):LiNbO3 crystals were produced by the VTE under different temperatures from 1010 to 1130 °C for different durations up to 395 h, the crystalline phase contained was determined by X-ray powder diffraction and their surface compositions were determined from the measured birefringence. The results show that the Li-deficient crystal keeps the LiNbO3 phase. The surface Li2O-content has an Arrhenius relationship to the VTE temperature and a square-root dependence on the VTE duration. Based upon the VTE temperature and time dependences of surface Li2O-content, the solution to the thermodynamic VTE is obtained and verified experimentally. The solution is crucial to design and produce a Li-deficient MgO:LiNbO3 crystal with desired Li2O-content profile. By using the solution, one can predict the Li2O-content depth profile after a certain VTE time for a given VTE temperature. [Copyright &y& Elsevier]

Abstract: Rare-earth-doping and various post-growth heat treatments effects on OH− absorption in singly Er- and Yb-doped, doubly Er/Mg- and Er/Yb-doped LiNbO3 crystals have been investigated. The OH− absorption in the rare-earth-doped crystals shows definite anisotropy and is stronger in a Z-cut plate. Rare-earth-doping causes considerable OH− absorption reduction. MgO-codoping induces additional reduction. Slight/heavy rare-earth-doping causes slight/considerable spectral shape change. Thermal reduction treatment causes OH− absorption vanishing whether the crystal is originally congruent or near-stoichiometric. Further oxidation treatment renders the absorption reemerged. Li-rich vapor transport equilibration (VTE) treatment causes significant absorption decrease. For a slightly rare-earth-doped Li-rich VTE-treated crystal, its spectral feature is similar to that of the undoped near-stoichiometric crystal; for a heavily rare-earth-doped VTE-treated crystal, its spectral shape preserves the feature of the heavily rare-earth-doped as-grown crystal. For the Er/Mg-codoped crystal studied, the Li-rich VTE also induces an abrupt conversion of peaking position from 3483 cm−1 to 3535 cm−1. The absorption in the Li-rich VTE-treated crystals also reveals aging effects in spectral shape, peaking position and absorption intensity. Li-poor VTE induces significant absorption increase. In addition, the effect of OH− presence on lifetime of Er3+ emission at 1.5 μm was also studied. The results show that the effect is small for the as-grown congruent crystals and slight for Li-rich VTE-treated ones. [Copyright &y& Elsevier]

Without any templates, hollow structured La 2 Mo 2 O 9 particles are successfully prepared at room temperature by an ageing-assisted salt solvent process. Powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy are used to investigate structure and morphologies of the obtained products. It is found that the ageing process has a significant influence on the particle morphology evolution when the mixed precursors are disposed at room temperature. With the ageing time changed from one week to 12 weeks, the particles morphologies evolve gradually from ellipsoid to sphere. The as-prepared hollow structured La 2 Mo 2 O 9 spheres have an average diameter of about 800 nm and shell thickness of about 100 nm. For elucidating the possible formation mechanism, the influences of the single salt on the particles morphologies evolution are also investigated. The final results indicate KCl is a key factor for formation of La 2 Mo 2 O 9 spheres and the formation of the hollow structure should have close relations with the surface tension in the ageing assisted process. [ABSTRACT FROM AUTHOR]

Ti-diffused near-stoichiometric(NS) LiTaO 3 multimode planar waveguide was fabricated by diffusion of Ti-film coated onto a congruent LiTaO 3 substrate and post Li-rich vapor transport equilibration process. The crystalline phase in the Ti-diffused layer was analyzed by powder x-ray diffraction and the Li 2 O-content was evaluated from the measured birefringence. The Ti-concentration profile was analyzed by secondary ion mass spectrometry. The modes guided in the planar waveguide were characterized by prism-coupling technique. The refractive index profile was constructed from the measured mode indices, and correlated with the Ti-concentration profile. The results show that the waveguide retains the LiTaO 3 phase and is in an NS composition environment. Both the refractive index and Ti-concentration follow Gaussian profile. The extraordinary and ordinary index change profiles are almost same, implying that the electric field profile of the mode guided in the NS Ti:LiTaO 3 waveguide would be polarization-insensitive. The ordinary and extraordinary index changes and the Ti-concentration follow a similar exponential relationship with a power index ∼1.3. Comparison shows that the Ti:LiTaO 3 waveguide shows considerable differences from the Ti:LiNbO 3 in Ti diffusivity, index change profile and its relation to Ti-concentration, and polarization dependence of guided mode. [ABSTRACT FROM AUTHOR]

Effects of finite hole depth and non-cylindrical hole shape on stop-band characteristics of photonic crystal formed by air-hole square lattice in Ti-diffused LiNbO 3 strip waveguide were studied theoretically. The study shows that hole depth determines the contrast of stop-band, and the hole radius and conical angle determine the bandgap and location. Cylindrical holes must be sufficiently deep so as to overlap most of waveguide mode and hence obtain a stop-band with high contrast, sharp edge and broad bandgap. Non-cylindrical holes seriously affect the stop-band features. Conical holes cause low contrast and narrow bandgap, and the stop-band shifts with the conical angle. For the cylindrical-conical hybrid holes, the cylindrical portion determines the desired features. Given the difficulty in fabricating high aspect-ratio cylindrical holes, we propose to fabricate the holes at the bottom of a shallow trench, which is introduced into waveguide surface prior to the hole milling. [ABSTRACT FROM AUTHOR]

Dispersion relation is established for Er(NbO 3) 3 phosphor, which is an excellent candidate for optical thermometry based on thermal effect of Er3+ fluorescence intensity ratio. To achieve it, Er(NbO 3) 3 phosphor was dispersed into α-bromonaphthalene liquid to form a suspension. Then, refractive index values of the suspension were measured at wavelengths 473, 589.3, 632.8, 980, 1311 and 1553 nm by dropping it onto a plastic sheet. Subsequently, refractive indices of the Er(NbO 3) 3 phosphor were evaluated from these measured index values using Maxwell-Garnett relation. Finally, based on these Er(NbO 3) 3 index values, which have an error 0.03, a three-oscillator Sellmeier equation that considers contributions from Nb–O group, plasmons in far UV regime and phonons in infrared region is established. In parallel, a Cauchy dispersion equation is also established. Both equations can well fit the experimental data and the refractive indices predicted by the two equations can be regarded as identical within the error 0.03. Refractive indices of Er(NbO 3) 3 phosphor at different wavelengths ranging from 473 to 1553 nm have been obtained from the index values measured from an α-bromonaphthalene mixture suspended with Er(NbO 3) 3 phosphor grains. A three-oscillator Sellmeier equation n2(λ) = B UV - B IR λ2 + B 3 /(λ 3 −2-λ−2) is proposed that considers the contributions from plasmons in far UV, phonons in infrared region and the Nb–O group. A Cauchy dispersion equation n(λ) = A + B/λ2 + C/λ4 + D/λ6 is also attempted to fit the experimental data. The fitting results show that both equations can give accurate prediction of the refractive index value of the Er(NbO 3) 3 phosphor and have an accuracy better than 0.03 satisfying the demand for Judd-Ofelt spectroscopic analysis. Image 1 • Refractive indices of Er(NbO 3) 3 powder were measured at different wavelengths. • A three-oscillator Sellmeier equation n2(λ) = B UV -B IR λ2+B 3 /(λ 3 −2-λ−2) is suggested. • A Cauchy dispersion equation n(λ) = A + B/λ2+C/λ4+D/λ6 is also established. • Both equations give accurate prediction of refractive index value of Er(NbO 3) 3. • Both equations have an accuracy 0.03 satisfying demand for Judd-Ofelt analysis. [ABSTRACT FROM AUTHOR]