Growth And Spectral Properties Of Rare Earth Er/Yb Co-doped Bismuth Silicate Crystals

Bismuth silicon oxide(Bi₄Si₃O₁₂,BSO)crystal,as a new type of scintillation material,has been applied in nuclear medicine and high-energy physics due to its advantages of short decay time and high radiation hardness.The growth technology of BSO crystal has been solved,and large-size crystals up to 200 mm can be grown using the modified Bridgman method.Rare earth-doped BSO has also been widely studied in scintillation,LED,and laser applications.Studies have shown that BSO crystal is an excellent laser matrix material.Among rare earth luminescent ions,Er³⁺and Yb³⁺are of great interest due to their ability to produce multi-wavelength lasers and high quantum efficiency,and they are a major research trend in the field of eye-safe lasers.Therefore,the desire to develop a new eye-safe laser material led to the study of Er³⁺and Yb³⁺co-doped BSO crystal（Er/Yb:BSO）.In this study,BSO crystal,Er³⁺-doped BSO crystal（Er:BSO）,and Er/Yb:BSO crystals with different ratios were grown using the modified vertical Bridgman method,and the spectral properties of the crystals were studied.The ratio was optimized,and the main research results are as follows:1.Pure BSO,Er:BSO,and Er/Yb:BSO crystals were grown in the modified Bridgman method according to the(Er_xYb_yBi_1-x-y)₄Si₃O₁₂ stoichiometric ratio,with compositions of x=0,y=0;x=0.2%,y=0.8%;and x=1%,y=0.The doped samples exhibited certain component segregation characteristics,and the crystals were light pink in color.The maximum size wasΦ25 mm×30 mm.The partition coefficients of Er³⁺and Yb³⁺in Er/Yb:BSO single crystals were determined by inductively coupled plasma atomic emission spectroscopy（ICP-AES）,which were 0.96 and 0.91,respectively.The transmittance spectrum of the crystals in the range of 200-2000 nm was tested,and the highest transmittance rate was close to 80%.The absorption and fluorescence spectra of the crystal in the range of 200-1700 nm were tested,resulting in an absorption cross-section of 6.96×10^-20 cm² and FWHM of 8nm at 976nm,and an emission cross-section of 0.9771×10^-20cm² and FWHM of 16nm at 1543nm.By fitting the fluorescence decay curve of Er³⁺in the ⁴I_13/2 state excited by 976nm,the fluorescence lifetime of Er³⁺at room temperature was determined to be 8.464ms.The above results indicate that compared with Er:BSO crystal,Er/Yb:BSO crystal has a wider FWHM and larger absorption cross-section,making it a potential laser material.2.BSO crystals co-doped with different concentrations of Er³⁺and Yb³⁺were grown by the modified Bridgman method.The ratio of Er³⁺and Yb³⁺was fixed at 1:9,while the doping concentration was adjusted to grow Er/Yb:BSO crystals with doping levels of 2 mol%（x=0.2%,y=1.8%）,3 mol%（x=0.3%,y=2.7%）,and 4 mol%（x=0.4%,y=3.6%）.The crystal size wasΦ25mm×50mm,and their transmittance was close to 80%.The X-ray diffraction peaks of the crystals exhibited a clear shift,indicating that Er³⁺and Yb³⁺entered the lattice of BSO crystal.The segregation coefficients of Er³⁺and Yb³⁺were 1.03 and 0.98 for 2 mol%Er/Yb:BSO,1.01and 0.95 for 3 mol%Er/Yb:BSO,and 0.58 and 0.54 for 4 mol%Er/Yb:BSO,respectively.The absorption spectra showed that the absorption peak of 3 mol%Er/Yb:BSO crystal was strongest at 976nm.The calculated absorption cross-sections of the three crystal samples at 976 nm were4.24×10^-20 cm^-2,2.99×10^-20 cm^-2,and 3.75×10^-20 cm^-2,respectively,with maximum FWHM of25 nm,28.32 nm,and 25.4 nm.The emission spectra showed that the emission peak of 3 mol%Er/Yb:BSO crystal was strongest at 1544nm.The absorption cross-sections of the three crystals at 1544 nm were 1.0250×10^-20 cm²,1.1452×10^-20 cm²,and 1.1050×10^-20 cm²,with maximum FWHM of 16nm for all three samples.These results indicate that the doping concentration affects the absorption and emission intensity of the crystals,but has no significant effect on the emission cross-section and FWHM.