Fluorescence and upconversion spectral studies of Ho3+ in alkali bismuth gallate glasses

The absorption and emission spectra of Ho3+ in alkali bismuth gallate glass matrices have been investigated in the visible and near-infrared. Strong fluorescence in the green (lambda similar to 549 nm), arising from the S-5(2) --> I-5(8) transition of the ion, has been observed when Ho-doped potassium bismuth gallate glass is optically-excited in the red (similar to646 nm). The measured quadratic dependence of the relative 549 nm intensity on pump power demonstrates that the upconversion mechanism is the sequential absorption of two photons. For a pump power of 285 mW at 646 nm, the upconversion efficiency is measured to be 5.5% which is among the highest values reported for glassy or crystalline matrices. (C) 2003 Elsevier B.V. All rights reserved.