Structure and Third-order Optical Nonlinearity Performance of Ge-Sn-Se Doped TiO$lt;inf$gt;2$lt;/inf$gt; Glass-ceramics at 1550 nm

TiO2 manifested as nucleating agent was introduced in Ge-Sn-Se ternary chalcogenide glass by heat-melt method. Then the samples were heat-treated for different time. The experiment results indicated that heat treatment process can lead to the precipitation of GeSe2 monoclinic crystals and SnSe2 hexagonal crystals in the TiO2 doped Ge-Sn-Se glass with the heat treatment time increasing. The variety of UV cut-off wavelength, optical band gap and Urbach energy revealed that the number of defect units in glass-ceramic samples increased with the increment of heat treatment time. The third-order optical nonlinearity of all samples was measured by Z-scan technology at 1550 nm. The results showed that the formation of nano-crystals in glass-ceramic samples can improve the third-order nonlinear refraction index significantly due to the strong local field effect. The largest value of nonlinear refraction index reached 5.75×10 -16 m 2 /W, and the sample heat-treated for 3 h was considered as a high-quality nonlinear optical mate-