Er³⁺-Based Diureasil Organic−Inorganic Hybrids

Erbium-doped organic−inorganic hybrids derived from different carboxylic acids (acetic, formic, and valeric) solvolysis have been prepared and characterized. The hybrid matrix (named as diureasil) is composed of a siliceous network grafted to both ends of a polymer chain containing about 8.5 oxyethylene units. Er 3+ ions have been incorporated as erbium triflate salt, Er(CF 3 SO 3 ) 3, with n = 5, 10, and 20, where n denotes the ratio of (OCH 2 CH 2 ) moieties of the hybrid organic counterpart per Er 3+ ion. Characterization techniques include X-ray absorption (EXAFS) at the Er L III -edge, Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. FT-IR studies reveal that both free and coordinated triflate ions exist in the hybrids, independently of the carboxylic acid used. Moreover, the “amide I” and “amide II” infrared spectral regions are deeply affected suggesting that the Er 3+ ions interact with the carbonyl groups of the diureasil matrix. EXAFS results show that the Er 3+ first coordination shell is composed by 10−11 oxygen atoms at an average distance of 2.30−2.32 Å. The Ω λ (λ = 2,4,6) intensity parameters were evaluated from absorption measurements together with the Er 3+ 4 I 13/2 state radiative lifetime (τ RAD ) and the peak emission cross section (σ EM ). Values obtained were Ω 2 = 12.3 × 10 −20 cm 2, Ω 4 = 5.56 × 10 −20 cm 2 and Ω 6 = 3.56 × 10 −20 cm 2, τ RAD = 3.6 ms and σ EM (1537 nm) = 1.0 × 10 −20 cm 2 . The host characteristic broad emission band in the visible and the Er 3+ emission at 1.5 μm were discerned. Bandwidth of ∼78 nm is observed for the latter emission which, together with the Ω λ, τ RAD, and σ EM spectroscopic parameters, denote the potential application of these hybrids in optical amplification devices.