The Luminescence Of Bi-doped Tungstate Crystals

In this thesis, we studied the luminescence of Bi-doped CdWO₄ single crystals, and made pilot study on Bi ions with what valence state in the crystal and the luminescence mechanisms for the emissions, effects of O2-annealing andγirradiation on the absorption, transmission and emission spectroscopic properties of Bi: CdWO₄ single crystals were explored primarily. Finally, we researched the immanent mechanism of change.In chapter one, the laser technology, the kinds and advancement of laser material and the application of activators are outlined. The developing history and the current research status of Bi-doped laser material were analyzed emphatically. We conclude the discovery of Bi in different research fields. Presents the three growth techniques about synthetic crystals——Czochralski method, hydrothermal method and Bridgman method.In chapter two, we studied the lattice structure and spectrum characterization of CdWO₄ single crystals, as well as the preparation method- Bridgman method of Bi: CdWO₄ crystals.In chapter three, we studied the luminescence of Bi-doped CdWO₄ single crystals. The absorption spectra, emission spectra and X-Ray photoelectron spectroscopy (XPS) of various parts of as-grown Bi: CdWO₄ crystal was investigated. The valence states and its distribution within the Bi: CdWO₄ were being inferred from the XPS. The luminescence mechanisms for the emissions were investigated primarily. The results showed that the Bi³⁺ and Bi⁵⁺ existed in Bi: CdWO₄ crystals simultaneously. The fluorescence emission of visible bands at 470 and 528 nm resulted from WO₆^6- in Bi: CdWO₄ and Bi³⁺ ions doped in the lattice, while the fluorescence emission of the near infrared band at 1078nm due to the Bi⁵⁺ luminescence. The emission intensity at 1078nm reduced and the content of Bi⁵⁺ ion decreased gradually; while the intensity at 528nm enhanced and the number of Bi³⁺ increased along the growing direction.In chapter four, we studied effects ofγirradiation on spectroscopic properties of Bi: CdWO₄ single crystals. The absorption, transmission and emission spectra of O2-annealed Bi: CdWO₄ crystals before and afterγ-irradiated were compared. The conclusion is as follows: The emission intensity at 1078nm reduced while the intensity at 528 nm enhanced after the crystals wereγ-irradiated. We can conclude that the valence state of Bi ions and their changes: Bi⁵⁺ transformation to Bi³⁺ ions through evolution ofγ-irradiated.In chapter five, we studied effects of O₂-annealing on spectroscopic properties of Bi: CdWO₄ single crystal. The Bi: CdWO₄ crystals were annealed at 500℃and 800℃temperature in O2 atmosphere. The color of the crystal became weak and the transmission of the crystal was enhanced obviously after O₂-annealed. The absorption, transmission and emission spectra of O₂-annealed Bi: CdWO₄ crystals before and after heat treatment were compared. The emission intensity at 1078nm reduced while the intensity at 528 nm enhanced after the crystals were annealed. We can conclude that the valence state of Bi ions and their changes with the variation of O2-annealed: Bi⁵⁺ transformation to Bi³⁺ ions.Finally, we concluded all the results that have been obtained in the paper, we realized the insufficiencies of our work, and anticipate the prospect of Bi doped emission materials.