Exploration On Crystallization Habit And Optical Property Of BaY₂F₈

Since the crystal BaY₂F₈,which is easy to be doped with rare earth elements,has many merits such as good transparent property, wider penetrating rang(0.125–15μm) and lower phonon energy, comparing with other host crystals it has been demonstrated to be suitable for up–conversion laser. On the other hand, being the trivalent rare earth element, Erbium (Er³⁺) which not only has rich energy levels, but also has other good characteristics, such as narrower luminescent band, higher capacity of absorption, higher efficiency of conversion and stable physical and chemical property, is being utilized and investigated as the active ion for laser materials both at home and abroad. In this thesis, researches mainly focus on the growth parameters of BaY₂F₈ and Er³⁺:BaY₂F₈ under TGT method, growth unit of BaY₂F₈. And the spectrum parameters of Er³⁺:BaY₂F₈ is also calculated.Based on the theoretical model of anionic coordination polyhedron growth unites and analyzed the crystal structure of BaY₂F₈, this paper studied crystallization habit of BaY₂F₈ from the spontaneous cooling. And presented the growth unites of BaY₂F₈ are eight--fold dodecahedral polyhedron with Ba²⁺ center and eight--fold dodecahedral polyhedron with Y³⁺ center. Two kinds polyhedrons' superposition formed BaY₂F₈ crystal. Using its XRD, making clear why {200},{130},{021},{330},{-111},{111},{221} and {002} faces are more growth. These things support with proof of applicability to the BaY₂F₈ crystal growth by anionic coordination polyhedron, and indicate a new growth method of BaY₂F₈ crystal in theory.The absorption spectrum was also measured and the several characteristic absorption peaks of Er³⁺ ions are clear. Using the J-O theory, the three phenomenological intensity parametersΩ_i ( i =2,4,6) were fitted, which were 1.43×10^-20cm², 0.49×10^-20cm² and 1.36×10^-20cm² respectively. The fluorescence decay times of Er:BaY₂F₈ crystal were analysed. The decay time of ⁴I_11/2 state is about 5 ms in Er:BaY₂F₈ crystal, which is quite longer than in oxide.