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Co-diffusion characteristics of Er3+ and Tm3+ ions in LiNbO3 crystal have been studied, together with two other properties: doping effect on refractive index of substrate, and Li out-diffusion. Er3+/ Tm3+-codoped LiNbO3 single-crystals were prepared by co-diffusion of stacked Er- and Tm-metal thin films, coated onto parts of the surfaces of X- and Z-cut congruent LiNbO3 crystal plates, at different temperatures and different durations in air. After diffusion, the surface refractive indices of the doped and undoped parts were measured by prism coupling technique, and the surface composition was evaluated from the measured indices. The results show that the dopings have negligible effect on the substrate index and the Li out-diffusion depends mainly on the diffusion temperature. The Er3+ and Tm3+ profiles were studied using secondary ion mass spectrometry, and a co-diffusion dynamical model is proposed and verified experimentally. From the measured profiles, the temperature-dependent Er3+/ Tm3+ diffusivity and solubility were obtained together with other relevant parameters, such as diffusion constant, activation energy, solubility constant and heat of solution. The Er3+ and Tm3+ co-diffusion exhibits similar temperature dependent diffusivity, and the dependence is similar to that of single-diffusion. In the co-diffusion case, the total solubility consists of two parts: Er3+ and Tm3+ parts, there is no anisotropy, and the value is equal to that of single-diffusion case, in which both ions have the similar solubility. The Er3+ and Tm3+ parts of solubility change relatively with the initial metal film thicknesses and hence have different temperature dependences. Nevertheless, their sum, i.e., the co-diffusion solubility, remains a constant at a given temperature. [ABSTRACT FROM AUTHOR]

Contribution of diffused Er3+ ions to refractive index of LiNbO3 crystal and relation of Li out-diffusion to Er3+-diffusion condition have been studied. Three X-cut and three Z-cut congruent LiNbO3 plates locally coated with 10, 15, or 20 nm thick Er metal films were annealed at 1100°C or 1130°C for 60 or 100 h under different atmospheres of surrounding air, wet O2 or wet Ar. After the anneal, the ordinary and extraordinary refractive indices at Er3+-doped and Er-free parts of crystal surface were characterized at the 633, 1311, and 1553 nm wavelengths by measurement of critical angle. The difference of surface index values at the Er3+-doped and Er-free parts enables to identify the Er3+-doping effect on substrate index. From the known birefringence, the surface Li2 O contents at the Er3+-doped and Er-free parts were evaluated. A comparison with the Li2 O content data before the anneal treatment allows to obtain the anneal-induced Li2 O loss and hence identify the anneal condition effect on the Li out-diffusion. The results show that the contribution of Er3+-doping to the ordinary index is within the measurement error of 1 × 10−3 and that to the extraordinary index is within ± 1.7 × 10−3, which is just slightly out of the measurement error. The diffusion temperature is while the diffusion environment is not the key factor responsible for the Li2 O out-diffusion. [ABSTRACT FROM AUTHOR]

The influence of Li-rich/ Li-poor vapor transport equilibration ( VTE) at 1100°C on surface Li2 O-content of 1 mm thick, congruent X- and Z-cut LiNbO3 crystal plates was studied against VTE duration. The VTE-induced surface Li2 O-content alteration was determined from measured birefringence. The results show that the induced surface Li2 O-content alteration has a square root dependence on the VTE duration for both cases of Li-rich and Li-poor VTE. The dependence shows a slight effect of cut of plate and is stronger for the Z-cut plate. The Li-rich VTE duration required for surface composition reaching the stoichiometric boundary is similar to 20.0/15.6 h for the X-/Z-cut plate. In contrast, the Li-poor VTE is a much slower process than the Li-rich VTE. The Li-poor duration required to reach the Li-deficient boundary is 400/323 h for the X-/Z-cut plate. Based upon the known VTE duration dependence of surface Li2 O-content, a mathematical model is established and the solution to the diffusion equation, an integral of error function complement, is obtained and verified by previously reported experimental results on Li-poor VTE. [ABSTRACT FROM AUTHOR]

Under Li-poor atmosphere, local Er3+ diffusion into highly MgO-doped LiNbO3 ( LN) crystal has been investigated. Three Z-cut 5 mol% (in growth melt) MgO-doped LN substrates locally coated with 44-60 nm thick Er-metal films underwent the respective Li-poor vapor transport equilibration ( VTE) treatment at 1060°C, 1100°C, and 1130°C for the same 90 h duration. After the VTE, the reductions of Li2O content at the Er-free and Er3+-doped parts of the surface of the three samples, determined from the measured birefringence, have a similar value of 1.0 ± 0.1, 2.0 ± 0.1, and 2.3 ± 0.1 mol%, respectively. Secondary ion mass spectrometry was used to study the Er3+ diffusion properties and the VTE effect on Mg2+ profile. From the measured Er3+ profiles, characteristic diffusion parameters such as 1/e diffusion depth, diffusivity, diffusion constant, activation energy, surface concentration, solubility, solubility constant, and heat of solution are determined. A comparison with the related results previously reported allows to conclude that heavy MgO-doping results in substantial decrease of both the diffusivity and solubility, and under the same diffusion temperature the diffusivity and solubility increase by as much as one order of magnitude and two times, respectively, as the diffusion atmosphere goes from the traditional argon to the Li-poor atmosphere. The Mg2+ profiles reveal that the VTE may induce MgO diffusion and hence an inhomogeneous profile in the Er3+-diffused layer. This undesired effect is strong for the 1130°C VTE temperature whereas is relatively much weak for 1060°C. It is tentatively explained in terms of the Er3+ diffusion and Li-poor VTE mechanisms. [ABSTRACT FROM AUTHOR]

Diffusivity at 1130°C of Li+ in LiNbO3 crystal in off-congruent, Li-deficient regime has been studied as a function of Li2O-content. A diffusion-limited Li2O-content reduction depth profile in an X- or Z-cut plate, ranging from 47.2 to 48.5 mol%, was produced by carrying out Li-poor vapor transport equilibration ( VTE) treatment on 1-mm-thick, initially congruent plates at 1130°C for 150 h. The profile was obtained by alternatively doing the optical polish to one crystal surface and the Li2O-content characterization on the polished surface through the measurement on birefringence. The Boltzmann-Matano mathematical analysis was applied to the profile to obtain the Li2O-content dependence of Li+ diffusivity. The results show that the diffusivity decreases with the decreased Li2O-content and the decrease is by at least one order of magnitude as the Li2O-content decreases by 1 mol% from 48.5 mol%. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near-stoichiometric regime, the diffusivity over the Li2O-content range from 47 to 50 mol% is presented. [ABSTRACT FROM AUTHOR]

Diffusion characteristics of Zr4+ in LiNbO3 single-crystal were studied. Zr4+-doped LiNbO3 crystal plates were prepared by in-diffusion of 100 nm thick ZrO2 film coated onto Z-cut congruent substrates in wet O2 at different temperatures. Zr4+-diffused profile was analyzed by secondary ion mass spectrometry. The results show that the Zr4+ diffusion follows the traditional diffusion theory. From the measured profiles, important diffusion parameters are obtained, such as diffusivity and its temperature dependence, diffusion constant, activation energy, surface concentration, and solubility. The Zr4+ has a diffusivity similar to that of Ti4+, implying that the Zr4+ doping and the Ti4+ diffusion can be performed simultaneously to simplify the fabrication process of a photorefractive-damage-resistant Zr4+-doped Ti-diffused LiNbO3 waveguide. [ABSTRACT FROM AUTHOR]

The influence of Li-rich vapor transport equilibration ( VTE) on surface Li2 O-content of 1-mm-thick, congruent X-, and Z-cut LiNbO3 crystal plates was studied against the VTE temperature. The VTE-induced surface Li2 O-content increase was evaluated from measured birefringence. The results show that the increase follows the traditional Arrhenius law with a surface Li2 O-content alteration constant (614 ± 136)/(91 ± 10) mol% and an activation energy (0.76 ± 0.05)/(0.53 ± 0.03) eV for the X/ Z-cut plate. An empirical expression that correlates the VTE-induced surface Li2 O-content alteration with both the VTE temperature and duration is presented. The expression is useful for producing a near-stoichiometric LiNbO3 plate with the desired surface Li2 O-content via balancing the VTE temperature and duration. [ABSTRACT FROM AUTHOR]