Study On Optical Properties And Microstructure Changes Of Glasses Induced By γ-ray Irradiation And Its Mechanism

Glass optics are important components of optical payload.When exposed to the space irradiation environment,the optical lens consisting of the systems will inevitably face the effect of cumulative radiations from high energy space rays,which will result in the decline of optical transmittance for the glass optics and thus cause the followed degradation of optical performance for the consisted optical systems.This is a key issue faced by all these optical systems that are loaded on the spacecrafts for long term space missions.To solve this problem,use of radiation-resistant optical glass materials for active anti-radiation reinforcement of space optical systems is a well-recognized and commonly adopted solution at home and abroad.The ground simulation experiments are used to study the changes in optical properties of optical glass materials induced by irradiations,and then to explore the mechanism of the produced changes from the perspective of the microstructure and defects of these materials,which can give important theoretical guidance for the research and development of radiation-resistant optical glass materials.This study can also be used to validate and guide the simulation of the radiation resistance of spatial optical playloads.This thesis’s work is based on the ZF series（ZF404,ZF504）,LaK3 series（LaK403,LaK503）,ZK509 radiation-resistant optical glasses and nonradiation-resistant SiO₂doped B₂O₃ containing phosphate glasses developed by our research group,and Co⁶⁰γ-ray is adopted as radiation souse to study theγ-ray total radiation dose and dose rate on the transmittance,refractive index,the microstructure,the types of defect centers and their concentration of the above mentioned optical glasses before and after irradiations,together with the measurements and analysis of transmission spectrum,refractive index test,Raman spectroscopy,X-ray photoelectron spectroscopy（XPS）,electron paramagnetic resonance spectroscopy（EPR）and magic angle spinning-nuclear magnetic resonance spectra（MAS-NMR）in order to explore the mechanism of changes in the properties and microstructure.The main research contents and results are summarized as follows:（1）Effects ofγ-ray irradiation on the spectral properties and optical band gap of the radiation-resistant optical glasses:The ZF series,LaK series,and ZK509 radiation-resistant optical glasses all showed good stability at their tolerated doses.As the irradiation dose increases,the ultraviolet cut-off edges of these glasses all gradually move toward the long wave direction and the transmittance of the short wavelength（<500 nm）decreases to different degrees.Nevertheless,the transmittance in long wave visible range is less affected.After irradiated by 10k rad（Si）γ-rays,ZF404 and LaK403 glass’s transmittance at 470nm decrease by less than 1%.After irradiated by 100k rad（Si）γ-rays,ZF504,LaK503and ZK509 samples’transmittance at 470 nm decrease by 1.87%,2.63%and 2.29%,and the optical density increments are 0.00982,0.01395 and 0.01153,respectively.When the total irradiation dose is 1×10⁵ rad（Si）（100k rad（Si））,with the radiation dose rate increase from 21.34 rad（Si）/s to 67.65 rad（Si）/s,within a unit of time,the energy received by the unit area of glass increases,and the internal temperature rises,which facilitates the recovery of the defect center,thus the transmittance at 530 nm is increased by 1%,2%and 1.8%for ZF504,LaK503 and ZK509,respectively,Besides,as the total dose of radiation increases,the optical band gap of the material decreases and the Urbach energy increases,which corresponds to an increase in the disorder degree of the glass network structure.（2）The effect ofγ-ray irradiation on the refractive index and micro-defects of the radiation-resistant optical glasses:When the total dose of radiation is increased from 0 to 100k,250k rad（Si）,the refractive indices of ZF504 and ZK509 increase,but the increasing trend decreases as irradiation dose change from 100k to 250k rad（Si）.While,the refractive index of LaK403 shows a decreasing trend with increasing irradiation dose（0-15k rad（Si））.The change in the glass’s refractive index is closely related to the corresponding change of the microstructure and defects in the glasses.For ZF504 glass,when the total irradiation dose is 100k rad（Si）,the transmittance decreases with a magnitude of less than 10^-4respect to the unirradiated sample.The maximum transmittance change of 2.3×10^-4 is observed at 486.1 nm.ZK509 has a relatively smaller change in refractive index than ZF504.When the total dose is 100 krad（Si）,the change in refractive index is less than1x10^-4.Increasing the irradiation dose to 250 krad（Si）,the changes also reach within the test error range of refractive index.When LaK403 is irradiated with a total dose of10krad（Si）,the refractive index decreases with the magnitude of 10^-5.Further,increasing the irradiation dose to 15k rad（Si）,the refractive index continues to decrease,reaching the order of 10^-4.（3）Effect ofγ-ray irradiation on microstructure and defects of radiation-resistant optical glasses:Raman spectroscopy tests show that the proportion of Q² groups in the ZF504 glass network decreases with the increase of the total irradiation dose,and the change of Q³is opposite.The proportion of non-bridge oxygen（NBO）also decreases with the increase of the total irradiation dose,indicating that theγ-ray breaks the Si-O bond in the glass network and causes the degree of polymerization of the glass network to decrease.EPR and absorption spectrum analysis demonstrate that the Pb²⁺⁺,Pb^2+–,F2color centers,and HC1 defects form under gamma irradiation,which contribute to the deterioration of the UV transmission performance of ZF4 glass.After heat treatment at410°C,the transmitted spectra of all irradiated samples almost coincided,and the transmittance was recovered.As ZK509 glass is irradiated with a total dose of 100k rad（Si）,the ratio of Q² and Q³ in the glass is almost constant.When the total dose of irradiation is increased to 250k rad（Si）,the proportion of Q² increases by approximately 1.6%.F color center and HC1are the main defect centers introduced by irradiation.For ZK509 glass,heat treatment near the glass’s transition temperature can effectively eliminate the defects induced by irradiation,so that the transmittance of the irradiated glass can be restored to the pre-irradiation level.When LaK403 glass is irradiated withγ-ray（0-20k rad（Si））,the degree of polymerization of the silicon-oxygen network structure increases and the degree of polymerization of the boron-oxygen network decreases.The fitting of EPR and absorption spectra show that when the irradiation dose is less than or equal to 20k rad（Si）,the transmittance of LaK403 glass is reduced mainly due to F2 color center and HC1 defects.When the irradiation dose increased to 100k rad（Si）,then BOHC and Al-OHC defects are generated,and Zr⁴⁺transferred to Zr³⁺by capture of electrons.These irradiation-induced defects contribute to the reduce in the transmittance in the short wavelength band（<500 nm）.（4）Effect ofγ-irradiation on properties of SiO₂-doped B₂O₃-containing phosphate glass:Doping of SiO₂ can enhance the network polymerization degree of B₂O₃-containing phosphate glass to some extent.When the ratio of SiO₂/B₂O₃ is less than4/1.5,the ratio of NBO and Q¹ tetrahedron in the glass decreases with the increase of SiO₂ content,while Q^2,Si increases.Further increasing the SiO₂ content to SiO₂/B₂O₃=6/1.5,the proportion of NBO increases.The reason is that a small amount of doped SiO₂ may enter into the phosphate network and thus increases its polymerization degree.Further increase of SiO₂ will form a Si-O-Si structure,which is independent of the phosphorus network,and the polymerization degree of the entire glass network is weakened.Afterγ-irradiation,the main microscopic defects in the glass include electron trapping defect centers（PO₄-EC（5.12 eV）、PO₃-EC（5.90 eV））and hole trapping defect centers（POHC1（2.31 eV）、POHC2（3.13 eV）和OHC（4.24eV））.The concentration of various defects increases with the increase of irradiation dose,but the growth rate of electron-trapped defects is faster than that of hole trapping defects.he electron capture center is the main radiation induced defect center whose concentration determines the location of the ultraviolet absorption edge.The hole trapping defects of POHC1 and POHC2 mainly affect the absorption in the visible region.As the hole trapping defects’concentration increases with the irradiation dose,the color of the glass gradually deepens to a reddish-brown color.