Transparent Oxyfluoride Glass Ceramics

Extract

Low-phonon energy glasses are desirable hosts for rare-earth (RE) ions because they enable emission from RE energy levels that would otherwise be quenched in high-phonon energy glasses. Such emissions are of interest for fiber amplifiers operating at telecommunications wavelength band s of 1.31, 1.46, and 1.55 μm, and for up-conversion lasers and three-dimensional displays.

Phonons are optical-frequency molecular vibrations in a material. If the RE energy level of interest lies only a few phonons in energy above the next lower lying level such as the ¹G₄ level of Pr³⁺, which is only 3,000 cm ⁻¹ above the ³F₄, only three Si—O vibrational phonons (1,100 cm−1) are required to bridge the gap as shown in Figure 1. Thus any electrons excited to the ¹G₄ level via an external pump source will be deexcited to the ³F₄ on down to the ³H₄ ground state via phonons, and no radiation of usable light will be produced. This is why emission from the ¹G₄ level of Pr³⁺ is absent in silicates and why researchers have gone to great lengths to make low-phonon energy glasses.