A comparison of the phenomena of photoluminescence and carrier-type reversal in Bi- and Pb-doped glasses

Hughes, M.A., Gholipour, B., Curry, R.J., Gwilliam, R.M., Homewood, K., Hewak, D.W., Elliott, S.J. and Lee, T.H. (2013) A comparison of the phenomena of photoluminescence and carrier-type reversal in Bi- and Pb-doped glasses. ICANS25, Toronto, Canada. 17 - 22 Aug 2013.

Abstract

We present evidence connecting the phenomena of carrier type reversal and photoluminescence (PL), which are observed in certain Bi- and Pb-doped glasses. We also report PL from Bi- and Pb-implanted glass, and that the order of the reaction which generates optically active Bi centers varies significantly between different glass hosts.

Comparing contour plots of PL spectra at various excitation wavelengths of Bi-doped chalcogenide, Bi-doped germanate and Pb-doped germanate glasses, indicates that five absorption/PL bands are in approximately the same position. This suggests that very similar active centers are present in Bi- and Pb-doped oxide and chalcogenide glasses. In 4% and 10% PbO doped germanate glass, one and two crystallization temperatures, respectively, can be observed. This could be seen as being analogous to the phase separation observed in Bi-doped GeS glasses displaying carrier-type reversal when the Bi content is increased past 11 mol%. When excited at 782 nm, Bi- and Pb- implanted gallium-lanthanum-sulphide-oxide (GaLaSO) glass thin films display PL bands centered at 820 nm and 860 nm, respectively. The intensity (I) of the 820 nm PL band has a power law dependence on Bi dose (d) of d1.4; a similar power-law dependence occurs in a Bi melt-doped oxide glass. When excited at 514 nm, Bi-implanted GaLaSO thin films display a PL band at 700 nm, which is not present in a Bi melt-doped chalcogenide glass having a similar composition to the implanted glass. This indicates that new Bi centers are formed through implantation, which are absent in the melt-doped glasses. This has important implications for Bi-doped glass lasers, in which the control of Bi centers is critical for improving performance. We report Bi-related red PL bands in Bi-implanted bulk Ge₃₃S₆₇ and Ga₅Ge₂₅S₇₀ glasses, and NIR PL bands in Ge₂₃Ga₁₂S₆₄Bi₁ glass; all of which have very similar compositions to those in which carrier-type reversal has been observed. This indicates that Bi-related PL and carrier-type reversal may be caused by the same Bi centers.

We determined the reaction order for the generation of Bi centers in various oxide glass hosts by extracting absorption data from previously published work, and measuring the gradient (equivalent to the power-law factor) of a double-logarithmic plot of Bi-related absorption coefficient against Bi₂O₃ doping concentration. The reaction order in Bi-doped oxide glasses decreased with increasing optical basicity of the glass host. A sequential redox reaction involving the decomposition of Bi₂O₃ into BiO, then Bin clusters, can explain a reaction order dependence on optical basicity. We suggest that red and NIR PL bands result from Bi²⁺ and Bin clusters, respectively, and these centers are also related to carrier type reversal.

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Contributors

Author: D.W. Hewak

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