Luminescent Properties Of Tb³⁺/Yb³⁺,Tm³⁺,Yb³⁺/Sm³⁺ Codoped LiYF₄ Single Crystals

With the development of the science and technology, researches on optoelectronic functional materials have made unceasing progress. Yttrium lithium fluoride crystal(YLF) is a new kind of matrix material. YLF single crystal doped with different rare-earth ions forms photochromic materials. In this work, the high quality optical material samples were obtained by an improved Bridgman method, which are YLF single crystals codoping the ion pairs of Tb3+/Yb3+,Tm3+/Yb3+ and Tb3+/Sm3+, respectively. Then, the structure of these samples was discriminated from their X-ray diffraction(XRD). And the optical properties of these crystals were evaluated from absorption spectra, excitation spectrum, emission spectra as well as decay curves. Besides, I-H theory was employed to verify the energy transmission mechanism and the luminescence property mechanism.In this study, the prolegomenon presents an overview of the research background, upconversion mechanism, downconversion mechanism as well as the property and assessment of white LED optical. It gives a brief introduction of the energy transmission and optical mechanism of rare-earth ions codoped solid materials. Meanwhile, it introduces YLF single crystal’s physics and chemical properties, optical performance and the growth method of crystal in detail, especially, detailed production process of YLF single crystal.In chapter two, the researcher explored XRD, absorption spectra, and emission spectra of YLF:Tb3+/Yb3+ to verify the structure, upconversion, mechanism and color rendering index of the crystal, respectively. The results demonstrate that when exposed to 960 nm laser, the crystal will mainly glow in the form of two-photons, which fulfills the upconversion luminescence of the yellowwish green light. Meanwhile, the crystal’s CIE chromaticity coordinates of luminescence spectrum shows(0.2874, 0.6733), and the color temperature is 6280 K with the color of yellowwish green light.Chapter three mainly introduces when Tb3+/Yb3+ codopes with series of YLF single crystals, quantum cutting from visible light to near-infrared light about 1000 nm will emerge. Based on XRD, the researcher ascertained the structure of Tb3+/Yb3+ codoped YLF. Moreover, the absorption spectra, excitation spectrum, emission spectra as well as decay curves of the sample were examined to explore its quantum cutting mechanism as well as the process of energy transformation.Chapter four mainly illustrates the downconversion luminescence mechanism of a series of Tm3+/Yb3+ codoped YLF single crystal samples that visible light at 465 nm can be converted into near-infrared light at 1000 nm. Fit analyses of the absorption spectra, excitation spectrum, emission spectra as well as decay curves of the above sample shows ions exist concentration quenching and the quantum efficiency of the energy transfer between Tm3+ and Yb3+ is not that high as expected.Chapter five focuses on luminescence performances of Tb3+/Sm3+ codoped YLF single crystal in visible wavelengths. The results indicate that the series of crystals simultaneously emit light of different colors under the irradiation of ultraviolet light, producing white light. The crystal will hopefully serve for new white LED materials.Chapter six summarizes the content and key results of the experiments, and proposes some simple plans and suggestions for future researches.