Spectral Properties And Frequency Upconversion Characteristics In Rare Earth Doped Kyw Crystal

Rare-earth doped upconversion materials have a wide range of applications in many areas, such as optical data storage,3-D display, bio-medical diagnosis and optical communication.The spectral properties and upconversion luminescence characteristics of Er³⁺-doped and Er³⁺/Yb³⁺-codoped KY(WO4)2 (KYW) crystal have been studied in the thesis. The experimental and theoretic results have particularly great importance for the application of laser amplifier devices, upconversion devices etc. As follows are the main contents in the paper.1. Based on Judd-Ofelt (J-O) theory, the J-O intensity parameters were calculated using the emission spectrum of Er³⁺:KYW crystal. The J-0 intensity parameters have been used to calculate the radiative transition probabilities of the Er³⁺ ions.The upconversion luminescence characteristics of Er³⁺:KYW crystal exciting at 980 nm were studied. Base on the rate equation theory and the energy level structure of Er³⁺ ions system, a model for the dynamics of frequency upconversion in Er³⁺:KYW crystal was proposed. The upconversion coefficients (C22 and C33) were estimated by numerically solving the rate equations and fitting simulated curve to the experimental fluorescence decay curve of 1550 nm and 980 nm emission.2. Absorption and emission spectra of Er³⁺/Yb³⁺:KYW crystal for the three principal optical axes were investigated at room temperature. The absorption and emission band intensities distinctly reveal the anisotropy of Er³⁺/Yb³⁺:KYW crystal. The electric dipole oscillator strengths of various bands and intensity parametersΩt (t=2,4,6) were calculated for the three principal optical axes of the crystal by the modified Judd-Ofelt theory. The integrated absorption cross-sections at 980nm were analyzed for the three principal optical axes. The results indicate the anisotropy of the absorption and emission spectra of the crystal, the Np axis is the best pumped axis when the Er³⁺/Yb³⁺:KYW crystal acts as a laser crystal.3. The upconversion spectrum and the fluorescence decay curve of Er³⁺/Yb³⁺:KYW crystal were measured.The upconversion characteristics and the energy transfer process of Er³⁺/Yb³⁺:KYW crystal were studied. A model for the dynamics of frequency upconversion process in Er³⁺/Yb³⁺ co-doped KYW crystal was proposed base on the rate equation theory and energy Level structure of Er³⁺/Yb³⁺ system. The Yb-to-Er energy transfer rate(P) and the upconversion coefficients (C22 and C33) were estimated by numerically solving the rate equations and fitting simulated curve to the experimental data.