Structural correlations and spectroscopic properties of rare earth doped fluorophosphate glasses and glass ceramics

Full text: Rare earth RE³⁺ doped fluorophosphates glasses and glass ceramics are among the most promising candidates for high efficiency laser generation in the near-infrared spectral region. Glass ceramics are advanced materials composed of one or more glassy and crystalline phases. By developing fluorophosphate base glasses with appropriate compositions and by controlling crystal nucleation and growth in them, glass ceramics with special properties can be fabricated combining the advantages of fluorides (low phonon energy, low refractive indexes, extensive optical window, lower hygroscopicity) and oxides (high chemical and mechanical stability and high dopant solubility), resulting in enhancement of the RE³⁺ emissive properties. In this study, we present the synthesis by melting/quenting and structural/spectroscopic investigation of new glasses and glass ceramics with composition 25BaF₂25SrF₂(30-x)Al(PO₃)₃xAlF₃(20-z) YF₃: zREF₃, where x = 20 or 25, RE = Er³⁺ an/or Yb³⁺ z = 0.25 - 5.0 mol%. Glass transition temperature (T_g), crystallization temperature (Tc), and melting temperature (Tm) were determined from the DSC thermograms.Longer lifetimes (t = 10 ms for Er³⁺ level ⁴I_13/2) imply high fluorescence quantum efficiencies h (up to 85%) for the glasses. Structural characterization by Raman and multinuclear solid state NMR spectroscopies indicate that the metaphosphate-type chain structure of the Al(PO₃)₃ vitreous framework is partially depolymerized and dominated by Q⁽¹⁾ units crosslinked by six-coordinate Al species. As revealed by ²⁷Al{³¹P} rotational echo double resonance (REDOR) NMR results the average local aluminum environment comprises 1.6 phosphate and 4.4 fluoride species. The studied glasses are promising starting materials for the fabrication of glass–ceramics with a high volume fraction of YF₃:Er³⁺ nano-crystals and very promising preliminary results indicate the feasibility of these new, advanced materials. (author)