Transparent TeO2-based glass-ceramics with graded optical nonlinearity such as second harmonic generation (SHG) have been fabricated for the first time through the two-step heat-treatment of 15K2O-15Nb2O5-70TeO2/7.5Li2O-7.5Na2O-15Nb2O5-70TeO2 joined glass sample. The gradual distribution of the species of alkali metal ions at the interface is confirmed from X-ray diffraction analyses. This result indicates the gradation of the second harmonic intensity at the interface, because the perfect solid solution between Na+ and K+ occurrs in the crystalline phase showing SHG and the intensity of second harmonicity decreases with increasing Na2O/K2O ratio. The fabrication of the transparent glass-ceramics having the gradient of the degree of the crystallization of the phase showing SHG has been also tried using the joined glass of 15K2O-15Nb2O5-70TeO2 (sample A) and 15K2O-15W2O6-70TeO2(sample B). Sample B is very stable thermally against crystallization. The crack is observed at the interface of such glass-ceramics because a large difference in the thermal expansion coefficient between the crystallized sample A showing SHG and the sample B maintaining the glassy state. The transparent Er3+ and Eu3+-doped glass-ceramics have been successfully prepared, and it is found that the intensity of the frequency upconversion fluorescence at around 550 nm due to the 4S3⁄2→4I15⁄2 transition of Er3+ in the glass-ceramics is strong compared with that in their precursor glass. This gives a new possibility for the fabrication of optically functionally graded TeO2-based glass-ceramics.
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Komatsu et al. (1998) studied this question.