The Properties Of Alkali Metal Ions (M⁺)/RE³⁺ Co-doped Upconversion Silicate Glass Ceramics

Rare earth (RE) doped transparent oxyfluoride glass ceramics usually with efficient luminescent properties, well transparency and optical properties, have been extensively studied owing to their potential applications in laser and fiber communication. Oxyfluoride glass ceramics are composed of oxide glass network and RE³⁺-doped fluoride nanocrystals. So far, the main fluoride hosts are bivalent fluorides, such as, PbF₂, BaF₂, CaF₂, ZnF₂ and CdF₂. When doped trivalent RE³⁺ ions substitute a part of the fluoride metal ions, the charge imbalance are caused nearby, as consquence, the upconversion luminescence efficiency will be confined. To compensate the charge imbalance, alkali metal ions were doped together with trivalent RE³⁺ ions which right play a roll in the exchange ions for waveguide manufacture.In this paper, the alkali metal ions Na⁺(or K⁺)/RE³⁺ codoped SiO₂-PbF₂-PbO glass and glass ceramics were prepared by high temperature sintering method. According to the results of Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), absorption spectra and upconversion luminescence spectra in the samples of Er³⁺ doped and Tm³⁺/Yb³⁺ codoped glass ceramics, we analysed the influence of the alkali metal ions on thermal stability, micro-structure and upconversion luminescence of the samples. And we obtained some useful results as follows:(1) In the first part, Na⁺(K⁺)/Er³⁺ codoped silicate glass ceramics were investigated. According to the XRD partern, Na⁺ ions are beneficary to the formation ofβ-PbF₂ nanocrystals in glass ceramics. The upconversion luminescence spectra measurements were carried out under the excitation of a 980nm laser diode (LD), and the intense red(650nm), green(520nm, 545nm) and violet(412nm) emission were simulataneous observed at room temperature. The doped alkali ions, expecially the Na⁺ ions enhance the emission intensity remarkably. With the increace of the Er³⁺ ions concentration, the ratio of red to green upconversion intensity decreased, whereas the ratio of violet to green upconversion intensity increased in Na⁺ doped glass ceramics.(2) In the second part, the TmF₃ and YbF₃ co-doped silicate samples were studied. The obtained precusor glass samples were all semitransparent and then changed to transparent after heat treatment. XRD and TEM measurements found some aggregations with the size of 50nm with a plenty of nanocrystals with the size of 2-3nm distributed inhomoginiously in the host glass. After heat treatment, the size of the crystals grew to 10nm, and the distribution became uniformly, which induce that the samples became tranparent. In K⁺/Tm₂O₃/Yb₂O₃ co-doped silicate glass ceramics, the K⁺ ions enhance the thermal stability and are of benefit to precipitate PbF₂ nanocrystals. Under the excitation of 980nm LD, the intense infrared (790nm), weak red(649nm) and blue(412nm) emission were simulataneously observed at room temperature. Particularly, the intensity of blue luminescence was improved in the 0.5mol%Na⁺/0.1mol%TmO_1.5/YbO_1.5 samples.It can be concluded that the upconversion luminescence intensty is obviously improved in RE+-doped SiO₂-PbO-PbF₂ glass and glass ceramics by doping alkali mental Na⁺ ions. And these Na⁺ doped host material would be of a potential applications in the up-conversion laser and fiber communications.