Study On The Self-crystallization Mechanism Of Ba₂LaF₇ In Silicate Glass-ceramics

Oxyfluoride glass-ceramics have many excellent characteristics,such as low phonon energy environment of fluoride crystals,good mechanical properties as well as oxide glass,good light transmittance and high solubility of rare earth ions.Therefore,oxyfluoride glass-ceramics can be used as the high-quality up-conversion matrix material.It can be widely applied to the fields of fluorescent display and laser as the up-conversion luminescent material by doping rare earth ions into it.This paper regards the glass system as a whole.From the perspective of glass synthesis,it mainly focuses on the three aspects of melt cooling(ie supercooling),melting temperature and composition adjustment.A study was conducted and the effects of composition adjustment and melting temperature change on the up-conversion luminescence properties of rare earth doped Ba₂La F₇ glass-ceramics were discussed.The main contents include the following three parts.(1)The effect of sub-cooling on the self-crystallization of Ba₂La F₇ in glass was studied.The melts of Ba₂La F₇ glass raw materials melted at the same temperature were cooled in air,room temperature deionized water and liquid nitrogen respectively;and the thermal process of heating the glass raw materials from room temperature to the melting temperature and then cooling to room temperature was tested.The different cooling media and different cooling rates only affected the growth of Ba₂La F₇grains.Ba₂La F₇ self-crystal nucleation occurs between 1100°C and 1200°C,that is,before the melt is poured into the cooling medium.(2)The effect of melting temperature change on the self-crystallization of Ba₂La F₇ in glass was studied.The melting temperature of the glass raw materials was gradually increased with a gradient of50°C.And the crystallization of Ba₂La F₇ in glass at 1350°C,1400°C,1450°C,and 1500°C was observed.When the melting temperature increases,the silicon-oxygen bond becomes longer,the fluoride in the raw material evaporates and loses,the crystallization activation energy of Ba₂La F₇ in the glass increases,and then the self-crystallization of Ba₂La F₇ weakens.The up-conversion luminescence performance of Er/Yb co-doped Ba₂La F₇ also gradually weakened as the melting temperature increased.(3)The effect of composition adjustment on the self-crystallization of Ba₂La F₇ in glass was studied.Different concentrations of Ti O₂were doped into the glass to change the internal structure of the glass.The crystallization of Ba₂La F₇ in the glass was observed after the internal structure of the glass changed.When the amount of Ti O₂ increased,its nucleation got enhanced,and more Ba₂La F₇crystal nuclei produced.At the same time,the silicon-oxygen bond in the glass is extended,and the self-crystallization of Ba₂La F₇ in the glass weakened.The up-conversion luminescent properties of Er/Yb co-doped Ba₂La F₇ also gradually weakened with the increase of the doped Ti O₂ concentration.