Upconversion Fluorescence Of Tm³⁺in YAG Glass Ceramics And Its Precursor Glasses

Upconversion fluorescence produced in rare-earth doped optical glass and glass-ceramics has broad application prospects in solid-state laser,high-density optical data storage,optical sensor and 3D display devices,and has attracted much attention.Among rare earth ions,Tm3+is the researcher's favourite because it can acquire a range of upconversion fluorescence from UV to near-infrared due to its abundant level structures.Yb3+ ions can match better with 980nm LD Lasers due to its special level structure,and are widely used as an sensitizer.In Tm3+/Yb3+co-doped system,Yb3+ can strengthen the upconversion fluorescence intensity of Tm3+ in matrix,which is beneficial for acquiring high-efficiency emission.However,now researches on matrix material is mainly focused on low phonon energy fluoride glass and transparent fluoride glass-ceramics,researches on silicate glass and its derived opaque glass-ceramics are insufficient.Compared with fluoride glass,silicate glass has better mechanical property,chemical stability and corrosion resistance.And the yttrium aluminium garnet glass ceramics derived from silicate glass are promising candidates in optical and lighting applications due to its smaller thermal expansion,more outstanding chemical-mechanical stability and lower radiationless relaxation loss.Therefore,the research on up-conversion luminescence behavior of rare earth ions in this matrix cannot be ignored.Based on this consideration,Tm3+/Yb3+ co-doped silicate glasses and its derived yttrium aluminum silicate glass ceramics have been designed and synthesized,and the upconversion fluorescence spectrum was investigated under 974nm laser excitation.The dependence of upconversion fluoresences intensity on the pumping power was described,structural characteristics of yttrium aluminium garnet glass ceramics and upconversion luminescence mechanism of Tm3+ ions were analysed.This research layed the foundation for developing the optical and illuminating devices from rare-earth doped materials.The followings are results this work achieved:1.Tm3+/Yb3+ co-doped yttrium aluminum silicate glasses have been synthesized.The structure of synthesized glasses is characterized,rare UV upconversion luminescence,strong blue and near-infrared upconversion luminescence,and weak red upconversion luminescence of Tm3+ irons were observed.Based on absorption spectrum,Judd-Ofelt parameters ?2,?4 and?6 have been derived to be 5.14×10-20,1.36×10-20 and 1.11×10-20cm2,respectively.Then we calculated the radiative transition probabilities,radiative lifetimes and fluorescence branching ratios.The maximum absorption and calculated emission cross sections are 1.960×10-20cm2 and 1.870×10-20 cm2 at 974nm,respectively.Based on the described dependence of upconversion fluorescence intensity on the pumping power,indicating that the UV emission are due to a four-photon excitation process,blue and red emission signals are due to a three-photon excitation process,and the near-infrared emission is due to a two-photon excitation process.2.Tm3+/Yb3+ co-doped yttrium aluminium garnet(YAG)glass ceramics have been synthesized by controlling the precursor glass to crystallize.The structure of yttrium aluminium garnet glass ceramics has been characterized,the primary particle size of YAG glass ceramics are calculated to be 46nm by using Scherrer Equation.The secondary particle size was determined to be 8?m through SEM picture,and the crystal grains are confirmed to grow with excellent orientation(444)in the glass matrix.Rare UV,strong blue and near-infrared,and weak red upconversion fluorescence of Tm3+ have been observed.Compared with the fluorescence spectrum of Tm3+ in yttrium aluminum silicate glass,the emission peaks in YAG glass ceramics are sharper,and the strongest emission peak is near-infrared.Obvious splitting peaks occurred in blue and near-infrared regions,indicating that the surroundings around Tm3+ ions have changed a lot in the process of crystallization.