Preparation Of Yttrium Aluminum Garnet,yttrium Oxide Based Ceramics And Single Crystals Doped Rare Earth Ions And Their Mid Infrared Spectroscopy

2-5μm mid infrared laser is located in atmospheric transmission window,molecular fingerprint area and thermal radiation energy concentration area.At the same time,it has strong water absorption.Therefore,it has important applications in many military and civil fields,such as infrared guidance,remote sensing,optical communication,atmospheric monitoring,biomedicine and so on.Yttrium oxide（Y₂O₃）and yttrium aluminum garnet(Y₃Al₅O₁₂,YAG)have great advantages in the 2-5μm mid infrared region.Y₂O₃ possesses stable physicochemical properties and excellent optical properties,as well as low phonon energy,which could reduce the transition without radiation relaxation.YAG owns optical isotropy,high symmetry and high thermal conductivity.Therefore,in this work,Ho³⁺and Dy³⁺ions are selected as activation ions,Yb³⁺and Tm³⁺as sensitization ions.YAG ceramics,Y₂O₃ ceramics and YAG single crystal are selected as matrix materials.The preparation,structure and spectral properties of the above laser materials are studied.The main research contents are as following:1.10at.%Yb,0.5at.%Ho:Y₂O₃ transparent ceramics with high optical quality were prepared by SPS.The highest in-line transmittance of Yb,Ho:Y2O3 ceramic sintered at1400℃reached almost 83%at 750 nm.The absorption spectra,fluorescence spectra and fluorescence decay curves at the room temperature were tested.The Judd-Ofelt parameters?₂,?₄ and?₆ were calculated to be 8.33×10^-20 cm²,1.81×10^-20 cm² and0.82×10^-20 cm²,respectively,and the spectral quality factor?₄/?₆ is 2.21.The intense emission cross section of Yb,Ho:Y2O3 ceramic was 3.43×10^-20 cm² at 2057 nm with FWHM of 208 nm.The fluorescence lifetime of the ⁵I₇ level was 10.621 ms and the quantum efficiency was 69%.The results show that Yb,Ho:Y₂O₃ transparent ceramics are potential 2μm laser gain media.Based on the upconversion luminescence of the sample in the visible band,Yb,Ho:(La_0.1Y_0.9)₂O₃ green upconversion ceramics were prepared by SPS.The temperature dependence of the upconversion luminescence intensity in the temperature range of 303-573 K was studied.The maximum relative sensitivity of the sample was 0.017 K^-1 at 573 K.2.xat.%Yb,0.5at.%Ho:YAG（x=5,10,15）single crystals were successfully grown by micro-pull-down method.Based on the powder X-ray diffraction data,the cell parameters of crystals under different Yb³⁺concentrations were calculated,and it was found that with the increase of Yb³⁺ion concentration,the crystal unit cell parameters decreased.The results show that the dopant ions Yb³⁺and Ho³⁺well replace the Y³⁺in the dodecahedral site in the matrix structure.The absorption spectra,fluorescence spectra and fluorescence decay curves were tested at room temperature.The effects of Yb³⁺doping concentration on the structure,spectrum and fluorescence lifetime were analyzed.Under 980 nm excitation,the fluorescence intensity increases exponentially with the increase of Yb³⁺doping concentration.The strong double emission peaks are concentrated at the wavelength of 1947 nm and 2109 nm,corresponding to the ⁵I₇→⁵I₈transition of Ho³⁺ions.This broad emission peak means that the sample has a large tunability in the 2μm band.The fluorescence lifetimes obtained by single exponential fitting were 5.883 ms,5.378 ms and 4.740 ms,respectively.Based on experimental phenomena,15at.%Yb,0.5at.%Ho:YAG single crystal is more conducive to particle number inversion and energy storage,laser output and high-power operation.3.10at.%Yb,0.5at.%Ho,xat.%Ce:YAG（x=0,0.1,0.5,1）transparent ceramics were successfully prepared by high temperature solid-state sintering in oxygen atmosphere.When the doping concentration of Ce³⁺is 0.5at.%,the absorption cross section of the sample at 936 nm is 4.96×10^-20 cm²,which corresponds to the Yb³⁺:²F_7/2→²F_5/2 transition.Fluorescence spectra and fluorescence decay curves were tested and discussed.According to the J-O theory,?₂,?₄ and?₆ are calculated to be13.95×10^-20 cm²,3.94×10^-20 cm² and 0.87×10^-20 cm²,respectively,and the spectral quality factor?₄/?₆ is 4.53.When the doping concentration of Ce³⁺increases from 0at.%to0.5at.%,the emission cross section at 2094 nm increases from 5.67×10^-20 cm² to 7.26×10^-20 cm².Because the introduction of Ce³⁺ion changes the particle number distribution at Ho³⁺:⁵F₅ and ⁵F₄/⁵S₂ levels to a certain extent,the red upconversion luminescence is weakened.Therefore,the introduction of Ce³⁺ion can effectively inhibit its upconversion luminescence and enhance 2μm luminescence.10at.%Yb,0.5at.%Ho,0.5at.%Ce:YAG transparent ceramic has good spectral properties and is expected to become 2μm working substance of laser.4.2at.%Tm,xat.%Dy:Y₂O₃（x=0,0.1,0.5,1）transparent ceramics with high optical quality were successfully prepared by vacuum sintering.The XRD and SEM microstructures were analyzed in detail.When the doping concentration of Dy³⁺is 1at.%,the corresponding absorption cross section of the sample at the ³H₆→³H₄ energy level is0.53×10^-20 cm²,and the FWHM is 43.59 nm.According to the J-O theory,?₂,?₄ and?₆are calculated to be 9.02×10^-20 cm²,0.75×10^-20 cm² and 0.64×10^-20 cm²,respectively,and the value of?₄/?₆ is 1.14.Under the excitation of the 793 nm LD pump source,the 2.9μm fluorescence intensity of the Dy³⁺:⁶H_13/2→⁶H_15/2 transition is enhanced when the concentration of Dy³⁺in the doped example increases,and the corresponding emission cross section is 3.63×10^-21 cm²,FWHM is 355 nm.The fluorescence lifetimes of Dy³⁺:⁶H_13/2 energy level were 357μs,282μs and 149μs,and the fluorescence lifetimes of Tm³⁺:³F₄ energy level were 4.878 ms,462μs,104μs and 61μs,respectively,by single exponential fitting.The results show that the Tm³⁺ion is an efficient sensitizer,which can reduce the filling of the Tm³⁺:³F₄ energy level and enhance the emission of the Dy³⁺:⁶H_13/2→⁶H_15/2 transition.Furthermore,the possible energy transfer mechanism between Tm³⁺and Dy³⁺ions is discussed in depth.The results show that Tm³⁺ions can not only increase the absorption efficiency of the pump source energy by Y₂O₃ ceramics,but also enhance the mid infrared luminescence of Dy³⁺ions at 2.9μm through efficient energy transfer,which is a 2.9μm mid-infrared laser for Dy³⁺ions in Y₂O₃ ceramics.The output provides further possibilities.