Optical and spectroscopic characterization of Nd-doped aluminosilicate fiber preforms made by the MCVD method using chelate delivery

4 F_3/2 level of Nd³⁺ in aluminosilicate optical fiber preforms after 807-nm excitation are reported in the temperature range from 15 °C to 500 °C for Nd₂O₃ concentrations in the range from 0.2 to %wt]0.9 and Al₂O₃ concentrations of between %wt]3.8 and %wt]8. At room temperature it is observed that for concentrations of less than %wt]0.6 Nd₂O₃ the fluorescence decay is approximately exponential; for the higher Nd₂O₃ concentrations the decay is increasingly bi-exponential. We have identified a “slow” (≈500 μs) and a “fast” (≈100 μs) decay time; the slow decay is attributed to isolated ions and the faster decay to energy transfer between homogeneously dispersed ions. The measured 1/e folding fluorescence decay time τ decreases slowly at a constant rate of -0.08±0.007 μs/K for %wt]0.9 Nd₂O₃. It is shown that increasing the Al₂O₃ concentration tends to suppress this temperature quenching effect. A radiative decay time of 640 μs is obtained by Judd–Ofelt analysis. Received: 24 October 1997/Revised version: 2 February 1998