Optical properties of erbium-doped fluorochlorozirconate glasses

We report the optical properties of a fluorochlorozirconate (FCZ) glass with the composition 53% ZrF₄, 20% NaF, 3.5% AlF₃, 3% LaF₃, 0.5% InF₃, (20 ? x)% BaCl₂, x% BaF₂ with x varying from 0% to 2%, and doped with various amounts of trivalent erbium by the addition of ErCl₃. Annealing of the as-prepared glass in inert (N₂) or reducing (5%H₂ + 95%Ar) atmospheres at temperatures that ensure the conversion of the glass into a glass-ceramic by the nucleation of BaCl₂ nanocrystals, does not significantly change any of Er³⁺ related absorption and photoluminescence (PL) characteristics. We have carried out a Judd–Ofelt analysis of the absorption spectra and obtained Ω₂ = (1.92 ± 0.3) × 10^? 20 cm², Ω₄ = (0.88 ± 0.16) × 10^? 20 cm² and Ω₆ = (0.59 ± 0.08) × 10^? 20 cm², and also the radiative lifetimes of the ⁴I_13/2→⁴I_15/2, ⁴I_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 bands. The radiative lifetime from the Judd–Ofelt analysis for the ⁴I_13/2→⁴I_15/2 band is in good agreement with the experimentally measured PL decay time. The examination of the optical properties of powdered samples with different average particle size does not show any photon trapping effects. We have determined the spectral absorption and emission cross-sections and then estimated the possible spectral optical gain for varying degrees of relative populations of the ⁴I_13/2 and ⁴I_15/2 manifolds.     

Optical and selected thermal properties of samarium-doped fluorochlorozirconate (FCZ) glass-ceramics: Formation and growth of BaCl2 nanocrystals in FCZ glass-ceramics

Photoluminescence (PL) and conventional and modulated temperature differential scanning calorimetry (DSC and MDSC) experiments have been carried out on a typical fluorochlorozirconate glass and glass-ceramics doped with Sm³⁺ and Sm²⁺ introduced by the addition of SmF₃ and a reducing agent, NaBH₄, into the initial mixture of constituents. The nominal FCZ composition was 53% ZrF₄, 20% NaF, 3% AlF₃, 3% LaF₃, 1% SmF₃, 1% BaF₂, 19% BaCl₂ (molar percentages). Prior to DSC and PL measurements, some of the glasses have been heat treated (annealed at an elevated temperature) under different conditions, which has resulted in glass-ceramics containing BaCl₂ nanocrystals with a hexagonal and/or orthorhombic crystal structure, depending on the heat treatment conditions. Hexagonal nanocrystals may be obtained by a simple one step annealing process while the formation of orthorhombic crystallites requires sequential multistep annealing treatments. Long duration, low temperature annealing, required for the formation of orthorhombic BaCl₂ nanocrystals, leads to the appearance of an endothermic enthalpy peak at around 250 °C on the conventional DSC thermogram. Temperature modulated DSC experiments identify a clear glass transformation in this regions; and the endothermic peak has been attributed to the structural relaxation enthalpy in the host glass which is usually obscured by the thermal effects associated with the formation of BaCl₂ nanocrystals. The observed thermodynamic effects correlate with the suppression of the broad PL band around 900 nm, which is most likely due to Sm²⁺ ions near or in the “shell-region” of the glass surrounding the nanocrystals.