Search

Growth of Er3+‐doped 100‐nm thick LiNbO3(LN) films on Z‐cut LiTaO3(LT) single‐crystal by e‐beam evaporation and in‐situ anneal at 600–800°C was studied. Crystalline phase, crystallographic orientation, Er3+ spectroscopic properties, constituent element valence states, defects, Er3+ concentration and stoichiometry of the films were characterized. The results show that the films are in LN single‐crystal state and orient along with c crystallographic axis. Constituent elements Li, O and Er are present in their respective single valence states Li+, O2−, Er3+, while the Nb is in two valence states Nb5+ and Nb4+. The films have Li2O‐contents around congruent point. Antisite(NbLi4+) is the major defect. Its concentration decreases, while Li2O‐content, crystallinity degree, and fluorescence intensity increase with increased growth temperature. The presence of Er3+ in the grown films is in the form of LN crystalline phase. Its concentration is considerably lower than that in initial target material because of lower e‐beam evaporation efficiency of heavy Er3+. [ABSTRACT FROM AUTHOR]

Zr4+/Ti4+-codoped LiNbO3 plates were prepared by local codiffusion of stacked ZrO2 and Ti metal films coated onto Z-cut congruent LiNbO3 substrates in wet O2 at 1060°C. The metal and oxide films have different thicknesses and coating sequences. After diffusion, the Zr4+ doping effect on the refractive index of LiNbO3 and the Li2O out-diffusion issue were studied by the prism coupling technique. The codiffusion characteristics of Zr4+ and Ti4+ were studied by secondary ion mass spectrometry. The results show that the Zr4+ doping has little contribution to the refractive index of the crystal. Li2O out-diffusion is not measurable. In the Zr4+-only diffusion case, the diffusivity of Zr4+ is four times smaller than that of Ti4+. In the Zr4+/Ti4+ codiffusion case, the Ti4+ codiffusion assists the Zr4+ diffusion. The Zr4+ diffusivity increases linearly by two more times with the increase in initial Ti film thickness from 0 to 200 nm. On the other hand, the Zr4+ affects the Ti4+ diffusion little. Neither the ZrO2 film thickness nor the coating sequence of Ti metal and ZrO2 oxide films influences the diffusivity of the two ions. All the codiffusion characteristics are explained. A Zr4+/Ti4+ codiffusion model is suggested that consists of two independent diffusion equations with a Zr4+ diffusivity dependent of Ti4+ concentration and a constant Ti4+ diffusivity. In addition, the existence of a waveguide in the Zr4+/Ti4+-codoped layer is verified experimentally, and the optical-damage-resistant feature of the waveguide is verified by two-beam hologram recording experimental results. [ABSTRACT FROM AUTHOR]

Diffusion properties of Sc3+ in LiNbO3 crystal were studied, together with other two related issues: Sc3+-doping effect on LiNbO3 refractive index and Li2 O out-diffusion arising from Sc3+ in-diffusion. To reach the goal, some Sc3+-doped LiNbO3 crystal plates were prepared by in-diffusion of Sc2 O3 film coated onto Z-cut congruent substrates in air at different temperatures ranging from 1030°C to 1130°C. After diffusion, the refractive indices at the doped and undoped parts of surface were measured by prism coupling technique and the surface composition was evaluated from the measured index. The results show that the Sc3+ doping has little contribution to the substrate index and the Li2 O out-diffusion is not measurable. The Sc3+ profile was analyzed by secondary ion mass spectrometry. Some characteristic parameters such as temperature-dependent diffusivity, diffusion constant, activation energy, and surface concentration are obtained. The Sc3+/ Ti4+ co-diffusion characteristics were also studied. Comparison shows that in the single-diffusion case, the Sc3+ diffusivity is considerably smaller than the Ti4+ diffusivity. In the Sc3+/ Ti4+ co-diffusion case, the Ti4+ co-diffusion results in substantial increase in Sc3+ diffusivity while the Ti4+ diffusivity changing little. The diffusion characteristics are qualitatively explained. The Ti4+-assisted Sc3+ diffusion would be utilizable in shortening the fabrication period of an optical-damage-resistant Ti-diffused LiNbO3 waveguide doped with Sc3+, and some considerations for the fabrication are given. [ABSTRACT FROM AUTHOR]

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]

Diffusion properties of Tm3+ in congruent LiNbO3 crystal have been investigated, together with other two related issues, i.e., Tm3+-doping contribution to refractive index of LiNbO3 substrate and Li out-diffusion. Four X-cut and four Z-cut congruent LiNbO3 substrates locally coated with 15-31 nm-thick Tm-metal films were annealed in surrounding air under different temperatures of 1030°C-1130°C for different durations of 20-70 h. After anneal, refractive index at Tm3+-doped and Tm3+-free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li2 O contents were evaluated from measured refractive index. The results show that Tm3+ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti4+- or Zn2+ doping. The Li2 O content at the Tm3+-doped surface equals that at the Tm3+-free surface. The Li out-diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out-diffusion is not measurable. At 1130°C, a 30-h diffusion procedure may cause 0.2-0.3 mol% slight loss of Li2 O content. Secondary ion mass spectrometry was used to study the Tm3+ diffusion properties. The results show that the diffused Tm3+ ions in all samples follow a complementary error function profile. From measured Tm3+ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er3+ diffusion. In comparison with Er3+ diffusion, the Tm3+ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm3+ has a lower diffusivity than the Er3+, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C. [ABSTRACT FROM AUTHOR]

We have measured the unpolarized and polarized emission spectra of 4 I9/2→4 I15/2 (810 nm) and 4 S3/2→4 I13/2 (860 nm) electronic transitions of Er3+ in LiNbO3 crystal under different incident directions and polarization states of excitation beam. From the measured emission spectra, the emission and absorption cross-section spectra were calculated based upon McCumber theory. It is found that Er3+ electronic transition shows interesting excitation beam direction effect in polarization dependence, spectral shape, and cross-section value. Both transitions are highly π-polarized as the excitation beam was aligned perpendicular to the optical axis of crystal while being highly σ-polarized as the excitation beam was oriented parallel to the optical axis of crystal. The spectral shape in the case of the perpendicular excitation is very different from that in the case of parallel excitation. The cross-section value in the perpendicular excitation case is at least 1.5 times larger than that in the parallel excitation case. These excitation direction effects are independent of the polarization state of excitation light, and are attributed to the selective Er3+ site excitation. In addition, the Er3+ 860 nm emission lifetime was measured to be 27 ± 5 μs and the quantum efficiency of the emission is 2.5%. [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]

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]

Fluorescence and absorption spectra at 530 nm (2H11/2→4I15/2), 560 nm (4S3/2→4I15/2), 660 nm (4F9/2→4I15/2), 980 nm (4I11/2→4I15/2), 1530 nm (4I13/2→4I15/2), and 2710 nm (4I11/2→4I13/2) of Er3+ in Gd3Ga5O12 single‐crystal codoped with Pr3+ have been measured. Judd‐Ofelt analysis yields the intensity parameters Ω2 = (0.68 ± 0.03) × 10−20 cm2, Ω4 = (0.60 ± 0.07) × 10−20 cm2, and Ω6 = (0.90 ± 0.17) × 10−20 cm2. A comparison with previously reported values of Er3+‐only doping case shows that Pr3+‐codoping causes slight change of both Ω2 and Ω4, while onefold increase of Ω6. From calculated radiative rates and measured fluorescence spectra, Er3+ emission cross‐section spectra were calibrated at first. Then, the absorption cross‐section spectra were calculated using McCumber relation. In parallel, the absorption cross‐section spectra were also obtained from the measured absorption spectrum, and compared with those obtained from the McCumber relation. The comparison shows that both methods give consistent result of absorption cross‐section spectrum. Further comparison with Er3+‐only doping case shows that Pr3+‐codoping causes considerable change of Er3+ cross‐section value. In spectrally mixing regions of Er3+ and Pr3+, Pr3+ emission affects little the determination of Er3+ emission cross‐section as Pr3+ fluorescence is much weaker than Er3+ fluorescence due to low Pr3+ concentration. [ABSTRACT FROM AUTHOR]

In the previous paper "Optical and Judd‐Ofelt spectroscopic study of Er3+‐doped strontium gadolinium gallium garnet single‐crystal" (J Am Ceram Soc. 2019;102:873–878), we have reported optical and Judd‐Ofelt spectroscopic properties of Er3+‐doped strontium gadolinium gallate (SrGdGa3O7) single‐crystal, and the Judd‐Ofelt study was performed on the basis of unpolarized absorption spectrum of the crystal. Present work reports the corrected unpolarized absorption spectrum and Er3+ concentration in the crystal, and hence corrected Judd‐Ofelt spectroscopic properties and cross‐section data. In addition, the polarization effect was considered in the Judd‐Ofelt analysis on the basis of polarization‐resolved absorption spectra. Effective Judd‐Ofelt parameters are presented and discussed in comparison with the results from the unpolarized spectrum, and consistent results have been obtained. This study also considers the effects of some other factors on the Judd‐Ofelt parameters. These include Er3+ concentration and selection of Er3+ absorption bands for the Judd‐Ofelt analysis. [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]

Er3+‐doped strontium gadolinium gallium garnet (SrGdGa3O7) single‐crystal was grown by Czochralski method. The Er3+ concentration in the crystal was determined as 4.2 × 1021 ions/cm3 by inductively coupled plasma atomic absorption spectroscopy. Refractive index of the crystal was measured at the wavelengths of 633, 1311 and 1553 nm by prism coupling technique. The results show that the crystal is a positive uniaxial crystal with a birefringence of ~0.01, and the Sellmeier equation reported previously for the crystal doped with Nd3+ is also valid for the one doped with Er3+. Unpolarized absorption spectrum of the crystal was measured at room temperature and the Er3+ absorption cross‐section spectrum was calibrated from it. The Er3+ spectroscopic properties were studied by Judd‐Ofelt theory. Some fundamental spectroscopic parameters were obtained that include absorption coefficient and cross‐section spectral distributions, electronic transition oscillator strength, Judd‐Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Noncongruent nearly stoichiometric/lithium‐deficient LiTaO3 crystal was grown by lithium‐rich/lithium‐deficient chemical vapor‐phase‐equilibration (VPE) technique, and low‐cost two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 instead of expensive LiTaO3‐Li3TaO4 or LiTaO3‐LiTa3O8 was used in the VPE experiments. The LiTaO3 crystalline phase in the lithium‐rich/lithium‐deficient crystal was confirmed by X‐ray analysis. The lithium‐rich/lithium‐deficient VPE‐induced lithium‐oxide (Li2O) molar content increase/reduction was measured as a function of VPE duration using gravimetric method, and empirical relations between them are presented for both cases. We show that both the lithium‐rich and lithium‐deficient VPE techniques based on the two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 can be successfully used to adjust the lithium‐oxide content in a LiTaO3 crystal and produce a noncongruent nearly stoichiometric or lithium‐deficient crystal plate with desired lithium‐oxide content. [ABSTRACT FROM AUTHOR]

A series of Mg2+/Er3+-codoped congruent LiNbO3 crystals were grown by Czochralski method from the growth melts containing 0.5 mol% Er2O3 while varied MgO content from 0.0 to 7.0 mol%. The unclamped electro-optic coefficients γ13 and γ33 of these crystals were measured by Mach-Zehnder interferometry. Two different voltage-applying schemes were adopted: one is the DC voltage applied to the crystal via Al films coated onto crystal surfaces and another is via a pair of external Cu slab electrodes. The coefficients measured by the two schemes show similar strong dependence on Mg2+ concentration. The dependence is non-monotonous, dramatic, and unusual, and reveals the features of two Mg2+ concentration thresholds of optical damage: one in the Mg2+ concentration range of 1.2-2.0 mol% (in crystal) and another in 4.5-5.0 mol%. Around the threshold the electro-optic coefficient decreases abruptly at first and then recovers quickly, and the coefficient drops by >20% (12%) at the first (second) threshold, which exceeds the error 3% considerably. The dramatic behavior is qualitatively explained on the basis of the EO coefficient model of LiNbO3 and the defect structure model for Mg2+-doped LiNbO3. [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]