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Crystallization behavior of the oxide semiconductor ZnO in zinc borate glass was investigated. The precipitated crystalline phase of glass ceramics containing a small amount of Al 2 O 3 was α -Zn 3 B 2 O 6 whereas that of the glass ceramics containing a large amount of Al 2 O 3 was ZnO. It was found that the c -oriented precipitation of ZnO in a glass ceramic was brought about by the in-plane crystal growth of needle-like ZnO crystallites along the a -axis. Amount of Al 2 O 3 that can make glass network affected the coordination state of B 2 O 3 in the glass, and a three-coordinated BO 3 unit was preferentially formed in the glass containing a higher amount of Al 2 O 3 . The present results suggest that crystallization of ZnO from multi-component glass is dominated by the local coordination state of the mother glass.

Langasite-type crystals such as Ba3Ga2Ge4O14 and BaGa4La2Ge2O14 are formed through the crystallization of gallium germanate glasses with stoichiometric compositions corresponding to langasite-type phases and optical properties of crystallized glasses are clarified. It is found that the single langasite-type phase is easily formed in each corresponding glass. The crystallized glasses with highly oriented langasite-type crystals at the surface are fabricated using an ultrasonic surface treatment method. The crystallized glasses with BaxGa5−xLa3−xGe1+xO14 phases show moderate second harmonic (SH) intensities of 5–75 times as large as α-quartz, and it is found that the SH intensity of BaxGa5−xLa3−xGe1+xO14 phases increases with the increase of the La3+/Ba2+ ratio. The feature of fluorescence spectra of Eu3+ ions incorporated into langasite-type crystals is also discussed.

Metastable BiBO3 and rare-earth (RE)-doped RExBi1−xBO3 crystals were prepared through the crystallization of 50Bi2O3 · 50B2O3 and xRE2O3 · (50−x)Bi2O3 · 50B2O3 glasses (RE = Y, La, Gd, Yb), and their second harmonic (SH) intensities were examined using the Kurtz powder method. It was confirmed that BiBO3 has two different crystalline forms, i.e., BiBO3(I) and BiBO3(II), and that BiBO3(I) transforms into BiBO3(II) at temperatures around 500 °C. Both phases were found to be nonlinear optical crystals with a phase matchable character, and the SH intensity of BiBO3(II) powders was approximately 110 times as large as α-quartz powders. The incorporation of RE3+ into BiBO3(II) was confirmed from X-ray diffraction analysis, and in particular, GdxBi1−xBO3(II) showed an enhanced SH intensity of approximately 145 times as large as α-quartz.

Crystalline phases and second-order optical nonlinearities in crystallized glasses of (Na,K)NbGeO5 (i.e., xNa2O · (25−x)K2O · 25Nb2O5 · 50GeO2) are examined. The molar volume of the glasses decreases with increasing Na2O content, indicating that the glass structure of NaNbGeO5 glass is more compact compared with KNbGeO5 glass. The optical basicity of the glasses is 0.94–0.95, implying that chemical bonds among constituents ions are basically very ionic. (Na,K)NbGeO5 glasses exhibit a unique crystallization depending on the Na2O/K2O ratio. The main crystalline phase in crystallized NaNbGeO5 glass is the NaNbGeO5 phase. KNbGeO5 glass shows a prominent bulk nanocrystallization giving nanocrystals of the K3.8Nb5Ge3O20.4 phase. A glass with the composition of K3.8Nb5Ge3O20.4 also shows a bulk nanocrystallization. The crystallized glasses with K3.8Nb5Ge3O20.4 and NaNbGeO5 crystalline phases do not show a second harmonic generation (SHG) at room temperature. The nonlinear optical (Na,K)NbO3 phases showing a SHG are formed at the surface (∼5 μm) of crystallized glasses with x=15 and 20, giving an orientation of the (1 1 0) plane. The present study suggests the presence of mixed-alkali effect in the crystallization behavior of (Na,K)NbGeO5 glasses.

Crystalline phases and second harmonic (SH) intensities in crystallized glasses of K2O–Nb2O5–SiO2 are examined, and the correlation between them is clarified. Crystallization behaviors depend strongly on SiO2 contents, and three stable crystalline phases of KNbSi2O7, K3Nb3Si2O13 and KNbO3 phases are formed in fully crystallized glasses. The crystallized glasses consisting of only perovskite-type KNbO3 phase are fabricated in the glasses with high K2O contents such as 40K2O · 20Nb2O5 · 40SiO2. The crystallized glasses containing KNbSi2O7 or KNbO3 phase show large SH intensities. The formation of K3Nb3Si2O13 phase is confirmed, and it is also demonstrated that this phase exhibits a second-order optical nonlinearity. Prior to the formation of three stable crystalline phases, it is found that various kinds of metastable crystalline phases showing second harmonic generations are formed. A transparent crystallized glass consisting of a metastable phase is fabricated.

New optical nonlinear transparent surface crystallized glasses have been successfully fabricated in the system of Ln2O3–Bi2O3–B2O3 (Ln=La, Sm, Gd). The second harmonic (SH) generation from the crystalline phases at the surface layers has been confirmed from Maker fringe measurements. It is suggested that the optical nonlinear crystals precipitated through the crystallization of Ln2O3–Bi2O3–B2O3 glasses would be new metastable BixLn1−xBO3 phases in which Bi3+ ions in BiBO3 are substituted by Ln3+ ions. The thickness of crystallized surface was approximately 5 μm and SH intensity was 0.02 compared with that of the Z-cut α-quartz with a thickness of 0.6 mm. In 12.5Sm2O3·30Bi2O3·57.5B2O3 glass, the crystalline dots with diameters of 5–65 μm are formed by the irradiation of CW YAG laser with a wavelength of 1064 nm (at 0.6 and 0.7 W, for 1–240 s), and it is found that these crystalline dots generate optical SH waves. This is the first finding on optical nonlinear crystalline dot formation by YAG laser irradiation in bismuth-containing glasses.

We report on crystallization and second- and third-order optical nonlinearities of a GeO2SiO2 glass poled with ArF laser irradiation. A large coefficient of the second-harmonic generation (SHG), d, is induced, which is accompanied by generation of crystallites in the glass. Even after the d-coefficient decays out, the crystallites and the third-order optical susceptibility, χ(3), are retained. The result suggests that origin of the large SHG induced in the glass is associated with the formation of space-charge field in large χ(3) area.

Second-order optical nonlinearity was induced by ultraviolet (UV)-poling in Ge-doped SiO2 thin films prepared by radio-frequency sputtering. Effects of sputtering, poling conditions and other treatment on the intensity and decay of second harmonic generation (SHG) were investigated. The d coefficient which is a measure of SHG intensity was found to depend on oxygen flow content during sputtering and on Ge-content with an optimum at around 1 cm3/min and 50 mol%, respectively. The UV-poling conditions largely enhance d coefficient which saturates at poling fields equal or larger than E p =1×10 5 V/cm and at total excitation energy of 1 kJ. Preannealing in vacuum enhanced d coefficient with the maximum of 12.5±0.6 pm/V was achieved by annealing at 500°C for 24 h. The addition of hydrogen prior to UV-poling largely improved the decay of d coefficient from several months to around 7 years.