We show that oxy-fluoride glass ceramics, with typical composition, 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2): 3.5(ErF3) mol % have potential applications in telecommunications. Upon heat treatment, Er3+ nucleates the growth of the nanocrystalline β-PbF2, which acts as its host. Heat treatment at 440 °C for 5 h and at 390 °C for 3 h gave rise to ∼12 and ∼2.5 nm diameter crystals, respectively. The emission band of Er3+ in the 1.54 μm telecommunications window (4I13/2→4I15/2 transition, at the half-height width) was 75 nm in the former and 90 nm in the latter case, while I13/24↔I15/24 absorption and emission bands became wavelength divergent in both cases. Also in the latter case, the spectrum was flat from 1.53 to 1.56 μm. The evolution of spectral behavior is explained by changes in average site geometry of the Er3+ dopant, related to the α→β phase transition of PbF2, which is stimulated by heat treatment.
The absorption coefficient of CuGeO 3 was measured in the energy range of 1-4 eV, in a temperature interval between 300 and 20 K, for light polarized along the b and c crystal axes. A weak absorption band at 1.7 eV is attributed to copper d-d transitions partially allowed by electron-phonon interactions; this is followed by a region of transparency leading to a strong exponential edge above 3 eV, which is identified with the onset of charge-transfer transitions. ͓S0163-1829͑96͒53040-7͔
Zinc tellurite glasses of compositions 19ZnO-80TeO 2 -1Ln 2 O 3 with Ln= Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f f transitions the Judd-Ofelt parameters V u were obtained. The values of the V u parameters are in the range usually observed for oxide glasses. For Nd 3 + and Er 3 + , luminescence spectra in the near infrared were measured and the stimulated emission cross sections | p were evaluated for some laser transitions. The high values of | p , especially for Nd 3 + , make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu 3 + doped glass were measured at 20 K, and the energies of the Stark components of the 7 F 1 and 7 F 2 states were obtained. A crystal field analysis was carried out assuming a C 26 site symmetry. The behaviour of the crystal field ratios B 22 /B 20 and B 44 /B 40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu 3 + sites appears to be very low compared to other oxide glasses.
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