Study of the effects of MeV Ag, Cu, Au and Sn implantation on the optical properties of LiNbO₃

We present the results of characterization of linear absorption and nonlinear refractive index of Au, Ag, Cu and Sn ion implantation into LiNbO₃. Silver was implanted at 1.5 MeV to fluences of 2 to 17×10¹⁶/cm² at room temperature. Gold and copper were implanted to fluences of 5 to 20×10¹⁶/cm² at an energy of 2.0 MeV. Tin was implanted to a fluence of 1.6×10¹⁷/cm² at 160 kV. After heat treatment at 1000 °C a strong optical absorption peak for the Au implanted samples appeared at approximately 620 nm. The absorption peaks of the Ag implanted samples shifted from approximately 450 nm before heat treatment to 550 nm after 500 °C for 1 h. Heat treatment at 800 °C returned the Ag implanted crystals to a clear state. Cu nanocluster absorption peaks disappears at 500 °C. No Sn clusters were observed by optical absorption or XRD. The size of the Ag and Au clusters as a function of heat treatment were determined from the absorption peaks. The Ag clusters did not appreciably change in size with heat treatment. The Au clusters increased from 3 to 9 nm in diameter upon heat treatment at 1000 °C. TEM analysis performed on a Au implanted crystal indicated the formation of Au nanocrystals with facets normal to the c-axis. Measurements of the nonlinear refractive indices made using the Z-scan method showed that Ag implantation changed the sign of the nonlinear index of LiNbO₃ from negative to positive.