Spectroscopic properties of Er3+–Yb3+ co-doped glass ceramics containing BaF2 nanocrystals

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Abstract

A Er3+ and Yb3+ co-doped transparent oxyfluoride glass ceramic containing BaF2 nanocrystals has been prepared. The formation of BaF2 nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er3+ and Yb3+ co-doped glass ceramic could be observed. Stark splitting of the Er3+ upconversion luminescence peaks in the glass ceramic indicated that Er3+ and Yb3+ had been incorporated into the BaF2 nanocrystals. Near infrared luminescence decay curves showed that the Er3+ and Yb3+ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.

Introduction

Rare-earth (RE) doped materials for upconversion luminescence are attractive for realizing the solid-state lasers and emissive displays in addition to their application in telecommunications [1]. The upconversion efficiency depends largely on the structure of the energy levels of RE ions and their local environments [2]. The key technique to design upconversion luminescence materials was to situate the RE ions in low-phonon-energy environment. Oxyfluoride glass ceramics have been developed as ideal RE ion hosts used for upconversion devices since 1993 [3], [4], [5]. Such materials combined the low-phonon-energy environment of fluoride crystals and the high chemical and mechanical stability of oxide glasses. Because of the nano-size of fluoride crystals these oxyfluoride glass ceramics remained transparent. However, these oxyfluoride glass ceramics were usually melted from poisonous regents such as CdF2 and PbF2. To find new highly efficient upconversion luminescence materials, we developed a novel series of Er3+ doped transparent glass ceramics containing alkaline-earth fluoride nanocrystals [6], [7], [8]. The alkaline-earth fluorides were important optical raw materials with high solubilities of both sensitizer and activator RE ions, which have been used successfully as the crystal laser hosts [9]. The alkaline-earth fluoride lattice consisted of a face-centered (fluorite) cubic structure. The F ions formed a cubic cage with the alkaline-earth cation residing at the center of each alternate cage. Trivalent rare earth ions could substitute for the divalent alkaline-earth cations [10] and the charge compensation was taken by the form of interstitial fluorine ions. In this paper, the Er3+ and Yb3+ co-doped glass ceramics containing BaF2 nanocrystals was reported. The upconversion and near infrared luminescence behavior of the Er3+ ions in the glass ceramics was discussed.

Section snippets

Experimental

The glasses with composition of 60SiO2–20ZnF2–20BaF2–5YbF3–0.5ErF3 and 60SiO2–20ZnF2–20BaF2–3.0ErF3 were prepared from high purity SiO2, ZnF2, BaF2, YbF3 and ErF3 raw materials. The batches of the raw materials were melted at 1400 °C for 45 min in a covered corundum crucible in the normal atmosphere. The molten glasses were poured between two copper plates, previously heated at 200 °C to limit thermal shocks. To obtain the glass ceramic sample, the glass was heated at 630 °C for 2 h. By using a

Results and discussion

Fig. 1 shows the DTA curve of the glass. The glass transition occurred at around 580 °C and a small crystallized peak began at 620 °C, centered at 670 °C and ended at 720 °C. It was found that the glass samples which were heated above 640 °C lost easily their transparency. To get transparent glass ceramic, the heat treatment temperature was selected to be 630 °C. Fig. 2 shows XRD patterns of the Er3+ and Yb3+ co-doped glass and glass ceramic that was prepared by heated at 630 °C for 2 h. XRD pattern of

Conclusions

A Er3+ and Yb3+ co-doped transparent oxyfluoride glass ceramic containing BaF2 nanocrystals was prepared by heating 60SiO2–20ZnF2–20BaF2–0.5ErF3–5YbF3 glass at 630 °C. The glass ceramic has high transparency due to smaller size of precipitated nanocrystals. Intense upconversion luminescence and the corresponding stark-split peaks could be observed for the glass ceramic, which indicated that Er3+ and Yb3+ had been incorporated with BaF2 nanocrystals. NIR luminescence decay curves showed that the

Acknowledgements

The authors gratefully acknowledge support for this research from the Science and Technology Department of Zhejiang Province (2006C14010), the Chinese-French Cooperation Programs (MX07-01) and Program for Changjiang Scholars and Innovative Research Team in University. This work has been partially funded by the French-Chinese Cooperation Programs EGIDE-PRA (No. 15558PB) and CNRS-PICS (No. 3601).

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