The Study Of Crystal Growth And Spectroscopic Properties Of Dy³⁺ Activated SrF₂ Laser Crystals

The～3μm laser is widely used in military countermeasures,medicine,satellite remote sensing,basic science and other fields.The yellow laser has important applications in ophthalmology,skin treatment,Yb lattice clocks,sodium laser-guided stars and lidar,etc.,and has become a current research hotspot.Based on the fact that Dy³⁺has both ⁴F_9/2→⁶H_13/2and ⁶H_13/2→⁶H_15/2energy level transitions,it can emit yellow and mid-infrared light simultaneously.Sr F₂crystal has low phonon energy,high thermal conductivity,high damage threshold and wide transmission band,and the crystal is easier to grow.Therefore,this paper selects Dy³⁺-activated Sr F₂crystals as the research object to study their yellow and mid-infrared spectral properties.The main studies are as follows.（1）The yellow and mid-infrared spectral properties of Sr F₂crystals monodoped with different concentrations of Dy³⁺have been investigated.Four Dy³⁺:Sr F₂crystals with different concentrations were grown by the Bridgman-Stockbarger method,and some spectroscopic tests were carried out on their sections,and spectral parameters and chromaticity coordinates were calculated.Comparison of the emission spectra and fluorescence lifetimes revealed that the Dy³⁺concentrations were heavily quenched and analysed as being due to dipole-dipole interactions between Dy³⁺.Among the four concentrations of crystals,the optimum doping concentration for yellow light emission was determined to be 0.5 at%with a FWHM of 10.8 nm,a fluorescence lifetime of 4.873 ms and an emission cross section of0.239×10^-21cm².The optimum concentration of mid-infrared luminescence is 2 at%.The mid-infrared emission spectra of the 2 at%Dy³⁺:Sr F₂crystal were tested at 909 nm and1272 nm photoexcitation,respectively,and the emission at 909 nm excitation was stronger than that at 1272 nm excitation,with⁶H_13/2energy level lifetimes of 0.881 ms,0.890 ms,and emission cross sections of 3.02×10^-21cm²,3.24×10^-21cm²,and the emission at 1272 nm can be matched with a commercial 1280 nm LD pump source,which is expected to achieve mid-infrared laser output.（2）The effect of co-doping with Yb³⁺on the mid-infrared spectral properties was investigated.Dy³⁺/Yb³⁺:Sr F₂crystals were grown and with the doping of Yb³⁺,the absorption of Dy³⁺/Yb³⁺:Sr F₂crystals at 975 nm was substantially enhanced and a 3.2-fold enhancement of emission at～3μm was observed,the emission bandwidth was slightly increased,the fluorescence lifetime of the Dy³⁺:⁶H_13/2energy level increased from 0.881ms to 1.154 ms.The emission cross section increases to 4.68×10^-21cm²and there is efficient energy transfer between the Yb³⁺and Dy³⁺ions with an energy transfer efficiency of 95.34%,analyzing ET2(Yb³⁺:²F_5/2→Dy³⁺:⁶H_5/2)as the main energy transfer pathway.The dramatic increase in performance shows that Yb³⁺can efficiently sensitize Dy³⁺,and that Dy³⁺/Yb³⁺:Sr F₂crystals have great potential for achieving lasing at～3μm under 975 nm LD pumping.（3）The effect of co-doping Tb³⁺and Eu³⁺on the performance of yellow light spectra was investigated.Dy³⁺/Tb³⁺and Dy³⁺/Eu³⁺:Sr F₂crystals with different concentrations were grown,and the emission and excitation spectra were tested to investigate the energy transfer between Dy³⁺and Tb³⁺,Eu³⁺.Comparing the emission cross sections,0.5 at%Dy³⁺/0.5at%Tb³⁺:Sr F₂showed an increase over the single-doped crystals at 0.306×10^-21cm²,while 2 at%Dy³⁺/0.5 at%Tb³⁺:Sr F₂has an increased lifetime of 2.108 ms with essentially the same emission cross section,favouring laser operation,with Tb transferring energy to Dy.In conclusion,the doping of Tb³⁺enhances the yellow emission of Dy³⁺and facilitates the realisation of yellow laser light.Although the emission cross section of Dy³⁺/Eu³⁺:Sr F₂is reduced in both concentrations compared to the single doped crystal,the emission and lifetime are enhanced in 2 at%Dy³⁺/0.5 at%Tb³⁺:Sr F₂,and Eu³⁺transfers energy to Dy³⁺with a transfer efficiency of 47.66%.The relatively small concentration of Eu³⁺is favourable to the yellow light performance.（4）The effects of co-doping with the non-optically inactive ions Gd³⁺,La³⁺,Lu³⁺and Y³⁺on the performance of yellow and mid-infrared spectra were investigated.By co-doping with non-optically inactive ions,both were found to result in a significant enhancement of the yellow light emission intensity and an increase in the emission cross-section,although the quantum efficiency and lifetime were reduced,but on balance,co-doping with non-optically inactive ions favoured the output of the yellow light laser,with 0.5 at%Dy³⁺/5 at%Lu³⁺:Sr F₂having a maximum emission cross-section of 1.221×10^-21cm²and being more suitable as a gain medium for the yellow laser.In the2 at%Dy³⁺/5 at%Y³⁺:Sr F₂crystal has an emission cross section of 3.55×10^-21cm²,a FWHM of 260 nm,a fluorescence lifetime of 1.062 ms,a quantum efficiency of 2.28%and a particle number inversion of P>0.4,promising a mid-infrared tunable laser output.In summary,co-doping with non-optically inactive ions increases the distance between Dy³⁺,attenuates the concentration quenching effect and enhances the yellow and mid-infrared luminescence performance.To sum up,this thesis focuses on the yellow and mid-infrared spectral properties of Dy³⁺single-doped and co-doped Sr F₂crystals for laser implementation,ultimately determining that 0.5 at%Dy³⁺:Sr F₂,0.5 at%Dy³⁺/0.5 at%Tb³⁺:Sr F₂,0.5 at%Dy³⁺/5at%Lu³⁺:Sr F₂crystals are more promising as yellow light gain medium for lasers,2at%Dy³⁺:Sr F₂,2 at%Dy³⁺/5 at%Yb³⁺:Sr F₂,2 at%Dy³⁺/5 at%Y³⁺:Sr F₂crystals are suitable as working substances for mid-infrared lasers.