Preparation And Performance Of Uranium Oxide Doped Luminescent Materials

UO₂ is one of uranium compounds with a cubic structure and its melting point of 2878?.UO₂ ceramic is an important nuclear reactor material,and UO₂ single crystal is also a potential functional material such as semiconductors,solar energy and thermoelectric.Due to its ultra-high melting point,radiative and variation of chemical valence,it is very difficult to grow UO₂single crystals.Scientists have used the floating zone method,cold crucible method,hydrothermal method,and other methods to explore the growth of UO₂ single crystals,however only small samples were obtained.Considering the rich 5f energy level of U ions,UO₂ exhibits potential applications as a luminescent material.In this thesis,we focus on the preparation and luminescent performance of uranium oxide doped Bi₄Ge₃O₁₂ crystals and borate glasses.The first chapter briefly introduces the research background of this thesis.The second chapter is the literature review.It introduces the U-O phase relationship,UO₂ crystal structure and optical properties,and summarizes the research progress of U-doped luminescent materials.Uranium oxides include UO₂,U₃O₈,U₄O₉,U₂O₅,UO₃,etc.Among them,UO₂ is the most stable,but there is a deviation of oxygen composition,forming a super-stoichiometric ratio.UO₂crystal mainly exhibit a cubic structure,with a band gap of 2.3 e V and a static dielectric constant of 5.53.U is often doped in ceramics,glass,crystal,and other materials in+3,+4,and+6valence states.U³⁺doped in Ca F₂ crystal emits 2-3-micron light and is expected to be used in mid-infrared laser crystals.U⁶⁺is often doped in ceramics,glasses,and phosphors to emit green light.The third chapter is about the growth and luminescence properties of UO₂doped BGO crystals.The UO₂ doped BGO crystals with different concentrations were grown by the Bridgman method and the crystals surface were brown.The transmittance of crystals is up to73.0%in the 500-2000 nm,the absorption edge is located near 290 nm,and the optical band gap is 4.05 e V.There is an excitation peak(strong intensity)at 293 nm,while the 0.01 wt%UO₂ doped BGO crystal has a weak excitation peak near 393 nm.The samples doped with other concentrations are not obvious.Under the excitation of the wavelength of 293nm,the intrinsic luminescence of Bi³⁺is still the main.When the 0.01wt%doped crystal is excited at 393 nm,there is a broad bound emission in the range of 400-700 nm,and the strongest emission peak is at 400 nm.Fitted peaks at 425,445,474 and 535 nm appeared by Gaussian fitting,and it is considered that U⁴⁺,Bi³⁺and U⁶⁺are excited to produce emission peaks.The fourth chapter is about the preparation and luminescence properties of UO₂ doped borate glass.UO₂ doped borate glass samples with different doping concentrations were prepared in the air by the melting method.To study the influence of U valence state on luminescence performance,we also melt UO₂ doped borate glass samples under N₂ atmosphere.Under N₂ atmosphere,the absorption peak of the sample conforms to the U⁴⁺characteristics.Choose 260 nm for excitation,and there are obvious emission peaks at 375,496,and 514 nm.Under air conditions,the sample has an emission peak near 523nm,and the emission intensity decreases with increasing UO₂ concentration.U⁶⁺exists as UO₆^6-structure in borate glasses.XPS analysis shows that U ions mainly exist in the form of U⁴⁺,U⁵⁺and U⁶⁺in the glass.