Growth And Spectroscopic Properties Of Er³⁺ And Er³⁺/Yb³⁺ Doped Potassium Lithium Tantalate Niobate Crystals

In recent years, the short wavelength blue and green solid state laser based on frequency upconversion (UC) rare-earth-ions-doping materials has attracted so much attention due to its wide applications and potential in the field of high density optical storage, color displays, photoelectron, and photoengraving, etc. The development of rare-earth doping single crystal materials has consequently become the foremost issue. The tungsten bronze-type potassium lithium tantalate niobate crystal is an excellent blue second harmonic generation crystal because of its broad non-critical phase-matching range, large nonlinear coefficients and photorefractive resistance threshold, etc. Therefore, it is of practical significance to grow the RE ions doped KLTN single crystal, and investigate its feasibility as laser crystal based on the upconversion luminescent properties.In the present dissertation, we have systematically studied the growth, basic physical properties, absorption, and photoluminescence in rare-earth (RE) doped KLTN crystals.By step-cooling method, we explored the compatible raw materials concentration ratio and growth temperature for Er doped KLTN crystal. Furthermore, we improved the crystal growth crafts and used the Czochralski method to grow the Er:KLTN and Er/Yb:KLTN crystals. The details of growth process and effects of growth craft were described in this thesis. The constituents of KLTN crystal were determined by means of the inductive coupled plasma emission spectrum (ICP) and energy dispersive spectrum analysis (EDS). The crystal structure was determined by the X-ray diffraction technique. The Curie temperature of crystal was measured by the differential thermal analysis (DTA) technique. Furthermore, the refractive indices of crystal were measured using the ellipsometry method, and the refractive indices dispersion was fitted using the Sellmeier equation.The ultraviolet-visible-near infrared optical absorption spectra were measured using the spectrophotometer. The absorption rule of crystal was described, and the ultraviolet absorption edges were determined. The Judd-Ofelt (JO) intensity parametersΩ_t (t=1, 2, 3) of crystal were calculated using the absorption spectra and JO theory. Moreover, the spontaneous emission probability, excited state radiative lifetimes, and fluorescence branching ratio of the Er³⁺ in the crystal were calculated.UC luminescence properties under 800 nm and 980 nm laser excitation were investigated systematically in Er³⁺:KLTN single crystals. The UC luminescence would be enhanced by the Er³⁺ concentration increase; moreover, the red emissions were enhanced more obviously than the green emissions. The UC processes were two-photon processes determined by pump energy dependence of the Er³⁺ UC luminescence intensities. The decay profiles of luminescence intensity investigations indicated that the green emissions were accomplished by ESA and ETU processes; the red emissions were accomplished by CR processes under 800 nm excitation, and ESA and ETU processes under 980 nm excitation, respectively. Furthermore, the UC mechanisms were provided. The UC emission rate equation model under 980 nm excitation was built and deduced to prove the change of pump power dependence. By comparing the fluorescence emission intensities of Er³⁺/Yb³⁺:KLTN single crystal under 400 nm and 800 nm excitations, a effective energy back transfer process from Er³⁺ to Yb³⁺ played the role in enhancing the red emission and weakening the 548 nm green emission.The Er³⁺ doped and Er³⁺/Yb³⁺ codoped KLTN ceramics were prepared by solid state synthesized method, and their fluorescence properties were investigated. The variations of the fluorescence spectra of KLTN ceramics with different Er³⁺ and Yb³⁺ concentrations were analyzed. The rate equation model was built and deduced to prove that the UC emission intensity changed with the increase of Yb³⁺ concentration. Furthermore, the arrangements of RE ions in tungsten bronze-type KLTN crystal lattice were investigated by the difference of the Er³⁺ fluorescence spectra in ceramics and crystal.In conclusion, the growth, physical properties, and spectroscopic properties of Er³⁺ doped and Er³⁺/Yb³⁺ codoped KLTN crystals are studied in the paper. The resultes show that Er³⁺ and Er³⁺/Yb³⁺ codoped KLTN crystals have excellent absorption and green upconversion propterties, they maybe have potential applications as a green upconversion laser crystal.