Second-order optical nonlinearities for the langasite-type phases obtained by crystallization of corresponding glasses are clarified for the first time. It is confirmed that most of langasite-type crystalline phases can be formed by crystallization in the corresponding glasses without introducting of any impurity phases, e.g., the glasses with the stoichiometric composition of Ba3Ga2Ge4O14, BaGa4La2Ge2O14, Pb3Ga2Ge4O14, etc. We find that Pb3Ga2Ge4O14 and Pb3AlGaGe4O14 phases exhibited strong second-harmonic intensities of approximately 100 times as large as α-quartz by means of a powder technique, demonstrating that those langasite-type crystals are excellent nonlinear optical materials. It is also suggested that the octahedral site is one of keys for second-order optical nonlinearity in langasite-type crystals.
2004 The Ceramic Society of Japan