| Under ion irradiation, the energetic ion will interact with both electrons and atoms in the materials and lose its energy via two nearly independent processes:(a) electronic energy deposition, which could induce the target-atom ionization and electronic excitation;(b) nuclear-energy deposition induced by nuclear collision, which could create a cascade of atomic collision events and displace the atoms from their initial sites. The former interaction is the dominate element during high energy ion irradiation process, and the latter will become more obvious once the ion energy is low enough, both of which could significantly change the physical and chemical properties of materials under certain conditions (fluence, temperature...). Nowadays the ion irradiation technique has been widely used in many hot research areas, such as biological radiation breeding, impurity doping of semiconductor, anti-wear and anti-eroding coat and cancer therapy.Based on the interaction between the irradiated ions and functional crystal materials, we carry out some research from three different aspects, including (i) the waveguide formation in optical crystals utilizing ion irradiation,(ii) the response properties of scintillation crystals to single ion excitation and (iii) damage behaviors of nuclear and optical materials under low and high energy ion irradiation. The main work in this dissertation is as follows:1. Optical waveguides, the fundamental and key element of the integrated photonic devices, are analogous to electronic systems but with higher information processing and transmission rate, which make them have many important applications in the telecommunication area. Waveguide lasers, waveguide amplifiers and laser sources utilizing SHG and OPO in nonlinear waveguides have attracted lots of attentions during recent years.Based on above-mentioned situation, we fabricate Nd:Li6Y(BC>3)3waveguides by using5MeV O3+or Si3+ion irradiation, respectively, which have typical "well"+"barrier" refractive index distribution and can effectively support the fundamental mode in visible and near-infrared telecommunication band through prism-coupling measurement. The studies of luminescence and Raman spectra demonstrate that Nd3+luminescence feature and crystal structure of the waveguide active region don’t change significantly and gain good preservation. Under the same conditions of irradiated energy and fluence, compared to the Nd:Li6Y(BO3)3waveguide formed by Si3+irradiation, the waveguide produced by O3+has a larger effective refractive index of fundamental mode and lower propagation loss, which could help us optimize the selection of irradiated ion species to produce the high-quality waveguide structure. In our work, LiTaO3waveguide has also been produced by swift Ar8+ion irradiation with low fluence. The surface damage and structure change along ion trajectory have been discussed based on RBS/channeling spectra and micro-Raman spectra. The threshold value of electronic stopping power for ion track formation in LiTaO3is evaluated using thermal spike model, which shows that the electronic stopping power in our experiment is large enough to induce the lattice amorphization along ion trajectory and further change the refractive index, and this is also the waveguide formation mechanism under swift heavy ion irradiation. Modal profile measurements through end-face coupling prove that the waveguide can support multimode waveguide in visible band and single-mode waveguide in near-infrared telecommunication band. The high irradiated energy generates a large thickness of the waveguide region, while the electron energy loss produces a large thickness of the optical barrier, which could effectively protect the light with near-infrared wavelength from coupling into the substrate based on tunneling effect, and play an important role in LiTaO3near-infrared waveguide formation.2. New inorganic scintillators with excellent response properties to irradiation energy are highly desirable to meet the increasing demands in various applications, such as advanced irradiation detectors in high energy nuclear physics, medical imaging, nondestructive inspection and astronomical observation. Due to the large penetration depth for x and y rays in materials, a high-quality scintillation crystal with large volume is necessary to completely absorb them, which has a high requirement for crystal growth and restricts the rapid evaluation of detector performance. It is worth noting that the candidate scintillator films can be readily prepared by various advanced deposition techniques, such as molecular beam epitaxy, electron beam evaporator and pulsed laser deposition, and their scintillation properties under ionizing-irradiation environment need to be identified quickly.Compared to x and y rays, irradiated ions can more effectively deposit their energy in a relatively small volume and then induce the luminescence emission, which could also be used to evaluate scintillation performance. Utilizing a TOF-scintillator-PMT setup, the response spectra of CaF2:Eu and YA103:Ce scintillators to H+, He+and O3+ions over a continuous energy range are measured. The light yield and energy resolution of YAlO3:Ce to single ion irradiation have been discussed, which shows that TOF-scintillator-PMT technique can be used to rapidly and effectively evaluate the scintillation performance of the radiation detector materials in forms of thin films or small crystals, and the related experiment data are beneficial for the selection of the optimum scintillator and therefore guide the bulk crystal growth. The energy partitioning process is used to analyze the scintillation intensity change of CaF2:Eu and YAlO3:Ce over the continuous excitation energy. The results clearly demonstrate that the scintillation response strongly depends on the excitation density in the irradiated region. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response (emitting the photons) and the nonradiative quenching process (heating the crystal lattice) under different excitation densities, which is also the main origin of the nonlinear response of the scintillators to irradiation.3. With the increasing of the energy needs and the security standards for nuclear power after Fukushima accident, the requirements for nuclear materials running safely for long period of time have prompted interests in advanced nuclear materials discovery, efficient screening techniques, as well as the fundamental research in understanding irradiation damage mechanism. Silicon Carbide (SiC), the key engineering material with good radiation tolerance, is considered to be used in the harsh (high temperature and strong irradiation) environment of the nuclear power, such as structural materials and fuel coatings in fission reactors, and structural components in fusion reactors. SrTiO3(titanate-based perovskite) is proposed as possible host materials for the immobilization of actinides and other long-lived fission products. Due to the irradiation damage will obviously change the physical and chemical properties of materials, it is necessary for us to study the damage behaviors of SiC and SrTiO3under irradiation environment.The damage accumulation curve of6H-SiC crystal irradiated by0.9MeV Si+at room temperature is determined through RBS/channeling spectra. The Si-disorders analyzed by2.0MeV He+and3.5MeV He+, respectively, could match with each other. We use0.9MeV Si+irradiation to produce several initial damage regions in4H-SiC crystal and then irradiate high energy ion (4.5MeV C2+,6.5MeV O2+,21MeV Si6+and21MeV Ni6+) to study the damage evolution. The C2+irradiation with the fluence of4×1015cm-2couldn’t induce any recrystallization and the corresponding displacement damage produced by C+starts to increase. The initial damage reduces after O2+irradiation with the fluence of1×101cm-2, which shows the recrystallization phenomenon existing in the damage area, and this process becomes very significant under Ni6+irradiation with the fluence of2×1013cm-2. The irradiation-induced recrystallization rate strongly depends on the electronic stopping power along ion trajectory, and will decrease along with the decreasing initial damage. The entire initial damage region will recrystallize simultaneously, which indicates that the interface between damage region and crystal region has no priority for this process.The damage behavior of SrTiO3crystal irradiated by0.9MeV Au+(used to simulate a-recoils) at room temperature has been studied. Four initial damage regions (Sr-disorder:0.07,0.29,0.54and0.67) are produced in SrTiO3utilizing0.9MeV Au+irradiation, and then irradiated by21MeV Ni7+(fluence:1×1011-2×1013cm-2). We find that the damage of Au+-irradiated region will increase so seriously under Ni7+irradiation. However, the Ni7+irradiation process with the same energy and the same fluence won’t produce any obvious damage in the virgin region (without Au+irradiation). This result shows that the irradiation of low energy ion with large mass number (a-recoil) could induce the crystal lattice instability of SrTiO3, which will make this material easier to be destroyed by the strong electronic energy loss during high energy ion irradiation process and this effect needs to be considered when we plan to use SrTiO3as the immobilization matrix for nuclear waste.LiNbO3is one of the most attractive and fundamental materials due to its outstanding acousto-optic, electro-optic and nonlinear properties, and has been widely used in the optical communication, data storage, laser technique and other optics yields. Recent studies have shown that during ion irradiation process, this crystal is very sensitive to the electronic energy deposition, so the damage behaviors of LiNbO3under low and high energy Si-ion (0.9MeV Si+and21MeV Si7+) irradiation are studied in this work and the results are as follows:The damage accumulation curve of z-cut LiNbO3crystal irradiated by0.9MeV Si+at room temperature is determined. The relationship between the surface damage and the fluence of21MeV Si7+has been discussed. The surface region of LiNbO3will become totally amorphous under21MeV Si7+non-channeling irradiation with the fluence of2×1013cm-2, and the damage will reduce (Nb-disorder:0.81) under21MeV Si7+irradiation with the same fluence but along channeling direction. For the same electronic stopping power, compared to higher energy ion, the track radius produced by lower energy ion is larger, which proves that the damage cross section depends on ion velocity. High energy Si7+irradiation will continue to increase the damage level of low energy Si+-irradiated region, and there is no recrystallization phenomenon for z-cut LiNbO3irradiated by high energy ion. Due to some basic models have been built to describe how the refractive index is affected by the lattice disorder, what we did could offer the necessary informations for LiNbO3waveguide formation through ion irradiation. |
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