Research Of Crystallization Characteristics And Luminescent Properties Of Oxyfluoride Glass-Ceramic Doped With(Pr³⁺,Yb³⁺)

In this paper, we use SiO₂, Al₂O₃, Na2CO3, CaF₂ Pr F3 and Yb F3 as raw material,then basic glass was prepared through high temperature melting and annealing processes, finally glass-ceramics of SiO₂-Na₂O-Al₂O₃-CaF₂ doped with(Pr³⁺,Yb³⁺)was prepared under different heat treatment systems. the forming ability,transmittance, phase composition, crystallization characteristic and luminescent properties which contact with components of raw material and manufacturing process was investigated by using DTA, XRD, SEM, FT-IR, spectrophotometer and other analytical testing methods, the results are as follow.The results of forming ability in basic glass shows: forming ability was enhanced with the increase of SiO₂/ A1₂O₃ and Na₂O / CaF₂ ratio, but weakened with the increase of Al₂O₃/CaF₂ ratio, According to the comprehensive analysis result,The optimum composition of this base glass is: 55 SiO₂-20Al₂O₃-5Na₂O-20 CaF₂?mol%?.The results of crystallization kinetics indicate that: during the crystallization process, the growth pattern of microcrystalline in the glass ceramic samples is threedimensional mechanism, which was mainly controlled by diffusion mechanism. But the nucleation rate sustained to decrease as the temperature rises, when the temperature rises to above 690 ?, it's already tends to zero nucleation, there are no formation of new nuclei; Cooling rate of Base glass analyze results showed that:Cooling rate has an impact on the appearance and microstructure of the basic glass,when the cooling rate is low, there are some initial nucleation generated inside glass,which will changed to hetero phase?calcium aluminum silicate?Al3Ca0.5Si3O11? phase?in last heat treatment processes, that cause devitrification phenomenon, also, the crystallization temperature was increased. On the contrary, for the base glass with higher cooling rate, It shows a single-phase crystallization mechanism in the post-crystallization treatment process, the precipitates behave perform as a single nanometer spherical CaF₂ nano-crystalline phase, corresponding glass ceramics has good transparency appearance.The results of DXR and SEM demonstrated that: the precipitation phase in this glass ceramic system is CaF₂ nano-crystalline phase, and the crystalline phase content and grain size will increase with the increasing of heat treatment temperature and heat treatment time, what's more, rod-like calcium aluminum silicate?Al3Ca0.5Si3O11? crystal phase will produced when the heat treatment temperature is exorbitant. As the results shows, The best heat treatment for this system is? coring system 580 ?, 0.5 h; crystallization system 670 ?, 3 h?; For Yb³⁺ doped glass ceramics, Yb³⁺ ions will join into the CaF₂ lattice then form Ca0.8Yb0.2F2.2 solid solution in the crystallization heat treatment process, moreover, crystalline phase content and grain size of CaF₂ crystalline in this glass ceramics will increase with increaseing of the concentration of rare earth ions.The results of absorption spectra and J-O theory shows that: the absorption spectra of rare earth ions have a performance that there is a simple superposition of the two peaks of Yb³⁺/Pr³⁺ in this co-doped system, and their absorption peak of rare earth ions do not change. There is a larger overlapping area between the emission cross section of Yb³⁺: 2F7/2?2F5/2 and the absorption cross section of Pr³⁺: 3H4?3P2,which indicated that the energy transfer is possible between Pr³⁺: 3P2 level and Yb³⁺:2F7/2 level. The results of luminescent characteristics shows: For the glass ceramics co-doped with Pr³⁺-Yb³⁺, the emission peak intensity in the visible regionois decreasing with the increase of Yb³⁺ ion concentration, yet the emission peak near infrared region increases, which shows in the excited state 3P0 level of Pr³⁺ ions will transfer more energy to the 2F5/2 ? 2F7/2 transition of Yb³⁺ ions then receive the near-infrared light, but when the Yb³⁺ ion concentrations reach to 8 mol%, we found that the near-infrared emission spectrum peak intensity of glass ceramic samples GC8 is lower than GC6, which attributed to concentration quenching phenomenon due to the concentration of rare earth ions inside the glass-ceramic is too large.The studies of energy transfer mechanism show that: compared with the auxiliary phonon energy transfer of Pr³⁺?Yb³⁺, the energy transfer between Yb³⁺?Yb³⁺ has a great energy transfer coefficient?CYb-Yb? values, it is mainly gain through resonance energy transfer mechanism, rely little on the assistance of phonon.Furthermore, the positive energy transfer coefficient of CPr-Yb in Yb³⁺/Pr³⁺ system is two magnitude orders extra than the reverse energy transfer coefficient CYb-Pr, which indicate that the dominated transfer process is positive energy transfer process of Yb³⁺?Pr³⁺,and its reverse process is negligible.