Growth And Properties Of Tm,Ho Doped Bi₄Ge₃O₁₂ Crystals By The Micro-pulling-down Method

The 1.5-2μm band laser has broad application prospects in early caries detection,laser surgery,laser processing,information encryption coding,lidar,and laser ranging.These have prompted researchers to continue to explore the 1.5-2μm band laser crystals with excellent performance.The absorption peak of Tm³⁺matches the emission wavelength of the commercial Al Ga As Laser Diode（LD）pump source well.The ³H₄→³F₄and ³F₄→³H₆transitions of Tm³⁺can produce 1.5μm and 1.9μm band lasers;Ho³⁺can be pumped by LD with wavelengths of 1.1μm and 1.9μm to emit 2μm（⁵I₇→⁵I₈transition）laser.This paper takes Tm:Bi₄Ge₃O₁₂（Tm:BGO）,Tm,Pr:BGO and Ho:BGO laser crystals with different doping concentrations as the research objects,and systematically studies the crystal growth,structure and spectral properties.The main research contents are as follows:1.Tm:BGO crystals with different doping concentrations（0.5 at.%,0.75 at.%,1.0 at.%,1.5 at.%and 2.0 at.%）were successfully grown by theμ-PD method.The crystal structure was tested by X-ray powder diffraction,and it was found that the structure of the Tm:BGO crystal did not change significantly,and it was still a cubic crystal structure.The unit cell parameters calculated by Jade software show that the unit cell parameters gradually decrease with the increase of the doping concentration.The absorption peak at 791 nm accordances well with the emission of the commercial Al Ga As LD pumping,and it increases with the increase of the Tm³⁺doping concentration.The emission bands centered at 1452 nm and 1879 nm of Tm:BGO crystal correspond to the ³H₄→³F₄and ³F₄→³H₆transitions of Tm³⁺,respectively.The emission intensity of the 1.9μm band increases with the increase of Tm³⁺doping concentration.The fluorescence lifetime of ³H₄level of Tm:BGO crystal decreases with the increase of Tm³⁺doping concentration,while the fluorescence lifetime of ³F₄level is relatively constant.2.Tm,Pr:BGO crystals with different doping concentrations(Tm³⁺:2 at.%,Pr³⁺:0.1 at.%,0.2 at.%,0.3 at.%and 0.5 at.%)were successfully grown by theμ-PD method.The crystal structure was tested by X-ray diffractometer.The unit cell parameter of Tm,Pr:BGO crystal is smaller than that of BGO crystal,but it gradually increases with the increase of Pr³⁺doping concentration.The deactivation effect of co-doped Pr³⁺on the lower ³F₄level of Tm³⁺1.5μm emission（³H₄→³F₄transition）was studied.With the increase of Pr³⁺concentration,the life of the upper energy level³H₄changes less,and the life of the lower energy level ³F₄decreases significantly.For the 0.5 at.%Pr,2 at.%Tm:BGO crystal,the energy transfer efficiency from the Tm³⁺:³F₄energy level to the Pr³⁺:³F₂energy level is 83.5%.The lifetime ratio of the upper and lower energy levels is 0.44,which is 11 times that of the Tm:BGO crystal,which indicates that Tm,Pr:BGO is a potential 1.5μm band laser gain medium.3.Ho:BGO crystals with different doping concentrations（0.25 at.%,0.50 at.%,0.75 at.%and 1.0 at.%）were successfully grown by theμ-PD method.The crystal structure of Ho:BGO is studied.It is the same cubic crystal structure as the BGO crystal.As the doping concentration increases,the unit cell parameters gradually decrease.The absorption of Ho³⁺at 1152 nm and 1943 nm well with the emission of the commercial LD.1 at.%Ho:BGO crystal has an absorption coefficient of 0.28 cm^-1at 1943 nm and an absorption bandwidth of 19.2 nm,which is very suitable for LD and Tm³⁺-doped laser pumping.The strongest emission of 1 at.%Ho:BGO crystal in the mid-infrared region is 2090 nm,the emission bandwidth is 174.0 nm,and the lifetimes of ⁵F₄+⁵S₂,⁵I₄and ⁵I₇energy levels are 19.40μs,9.73μs and 6.39 ms,respectively.