Investigation on crystallization and influence of Nd3+ doping of transparent oxyfluoride glass-ceramics
Introduction
Rare-earth doped transparent oxyfluoride glass ceramics, in which rare-earth ions selectively incorporated into the fluoride nano-crystals immersed in an oxide glassy matrix, can offer excellent luminescent properties due to the combination of the advantages of both fluorides and oxides: low phonon energy environment of fluoride crystalline for luminescent ions, and good mechanical and chemical properties of oxide matrix.1, 2 This new material has attracted great attention in the continuous research for the novel optoelectrionic devices.
Nd3+ is one of the most widely studied luminescent ions, and Nd3+ doped crystalline,3 glass4 and ceramics5 have been applied in many fields. Compared with other lanthanide ions, however, only a few works have been devoted to the research on Nd3+ doped transparent oxyfluoride glass-ceramics. It was reported that Nd3+ ions are difficult to be incorporated into crystalline phase for oxide glass-ceramics,6, 7 and Nd3+ doped oxyfluoride glass-ceramics containing Pb(Cd)F2 are susceptible to proceed spontaneous devitrification during glass preparation which was not observed when doping the same glass matrix with Er3+, Eu3+, Yb3+, or Tm3+ ions.8 The LaF3 crystals are considered to be a more suitable host for rare-earth ions than Pb(Cd)F2 because the solid-solubility of rare-earth ions can be superior, owing to the similar ionic radius and the same valence for La and other rare-earth ions.2, 9, 10 In this work, we studied the crystallization behavior and the influence of Nd3+ doping of oxyfluoride glass-ceramics containing LaF3 crystals.
Section snippets
Experimental
The glass-forming compositions are 41.2SiO2-29.4Al2O3-17.6Na2CO3-11.8LaF3-xNdF3 (x = 0, 0.5, 1, 2, 3 and 4) in mol%, accordingly, the samples are named in the following text as samples 1–6, respectively. High purity reagents (≥3N) were used as the starting materials. The mixed batches were melted in a covered platinum crucible under the air atmosphere at 1350 °C for 1 h. The melt was then poured into a copper mold to proceed rapid quenching. The obtained glassy samples with 3–4 mm thickness were
Thermal analysis
The as-made samples 1–5 were visually transparent, appearing blue-purple due to Nd3+. Sample 6 was translucent due to spontaneous devitrification during melt quenching revealed by HRTEM observation. Therefore, only samples 1–5 were further investigated in this work.
The DTA curves for the as-made samples with different NdF3 content are shown in Fig. 1. A unique exothermic peak appears for all the curves, indicative of the LaF3 crystallization from the glass matrix confirmed by XRD analysis. With
Conclusion
The crystallization kinetics was studied for 41.2SiO2-29.4Al2O3-17.6Na2CO3-11.8LaF3 glass samples with different NdF3 doping. After thermal treatment, only hexagonal LaF3 nano-phase crystallized from the glass matrix in a mechanism of diffusion-controlled growth process with zero nucleation rate. The doped Nd3+ ions incorporated into the LaF3 crystals resulting in the shrinkage of the lattice. Besides, they played the role as nucleating agent producing a downshift of crystallization
Acknowledgements
This work was supported by grants from the Natural Science Foundation of Fujian Province China (project no A0320001), the Ministry of Science and Technology of China (project no. 2003BA323C) and the State Key Laboratory of Structural Chemistry of China (project no. 050005).
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