The Study On Upconversion Luminescence Mechanism Of Femtosecond Pulse-Excited Mg:Nd:LiNbO₃

Nd:LiNbO3 crystal combines the excellent laser characteristics of the Nd3+ and the electro-optic and nonlinear optical properties of the LiNbO3 crystal. So it has attracted public attention. In this paper we utilize infrared transmittance spectrum and ultraviolet-visible absorption spectrum to investigate the structure of Nd:LiNbO3 crystals and Mg:Nd:LiNbO3 crystals, and the influence of Mg ions on the optical properties of the crystals were studied also. We utilize upconversion luminescence spectrum to analyse energy levels structure of rare earth ion and upconversion luminescence mechanism. Which is important for chooseing laser crystal material and improving the performance of short-wavelength solid-state lasers. The summary about this paper is as follows:First, the current research situation of rare earth-doped LiNbO3 crystal and upconversion luminescence is introduced, and the theory basis of the upconversion luminescence is deduced in detail.Second, Using infrared spectra, the threshold concentration and location of Mg in doped LiNbO3 crystals were confirmed, and the location model was given. The threshold concentration of Mg is between 3 mol% and 5 mol% in doped LiNbO3 crystals. Before the doped concentration of Mg achieves its threshold Mg takes NbLi, and when the doped concentration of Mg is over the threshold Mg enter NbNb and LiLi at the same time, resulting in absorption peak from 3 482 cm-1 to the 3 535 cm-1, and then come to Mg ion is the reasons of OH- absorption peak occurred purple shift. Using ultraviolet-visible absorption spectra, the intrinsic absorption edge of change and intrinsic absorption edge mobile mechanism were confirmed. It has the same conclusion with location model in the infrared spectrum. And also to draw Mg:Nd:LiNbO3 crystal absorption spectra of the absorption peak position and Nd:LiNbO3 crystal is basically the same conclusion.At last, Finally, according to sample ultraviolet-visible absorption spectra of the test results, respectively, select the 752 nm, 813 nm for excitation wavelength of light, to build the experimental optical path, and then select a different excitation power to test the Nd:LiNbO3 crystal and Mg:Nd:LiNbO3 crystal upconversion luminescence, using upconversion spectra, upconversion mechanisms and upconversion luminescence efficiency are analyzed.Comprehensive, Nd:LiNbO3 and Mg:Nd:LiNbO3 crystal can produce up-conversion luminescence in the femtosecond pulse excitation. under appropriate conditions have been better upconversion luminescence efficiency, is an excellent upconversion luminescence materials.