Design and Characterization of New Optical Functional Transparent Tellurite Glass-Ceramics

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The purpose of the present study is to clarify the mechanism of the second harmoinic generation (SHG) in transparent tellurite-based glass-ceramics which have been discovered by the present author's group. The following results were obtained. 1) The chemical composition of the crystalline phase showing SHG in 15K_2O-15Nb_2O_5-70TeO_2 glass-ceramics corresponds to K (Nb_<1/3>Te_<2/3>) _2O_<4.8> approximately, and its crystal structure is oxygen-defect fluorite type. This crystal is distorted slightly from cubic, maybe causing SHG.2) The lattice constant of the crystalline phase in xNa_2O- (15-x) K_2O-15Nb_2O_5-70TeO_2 glass-ceramics decreases linearly with increasing Na_2O content, meaning the appearance of the solid solution between Na^+and K^+. The intensity of SHG decreases steeply with increasing Na_2O/K_2O ratio, and the glass-ceramic with x=8 shows no SHG.3) The thermal stability against crystallaization in 15K_2O-xRO- (15-x) Nb_2O_5-70TeO_2, RO=WO_3, MoO_3, is extremely high, and the formation of the crystalline phase showing SHG tend to be difficult. 4) The surface crystallization layr generates strong second harmonic generation compared with the interior of the glass-ceramics. 5) The transparent Er^<3+>-doped tellurite-based glass-ceramics have been fabricated, and the upconversion at 550nm due to ^4S_<3/2>*^4I_<15/2> transition under the irradiation of laser with 800nm wavelength is clearly observed. 6) It is found from heat capacity changes at the glass transition that rearrangements among structural units occurs easily in tellurite-based glasses.