THE INFLUENCE OF SUBSTITUTIONAL DISORDER ON NONRADIATIVE-TRANSITIONS IN CR3-DOPED GALLOGERMANATE CRYSTALS()

The substitutionally disordered nature of gallogermanates creates a di stribution of crystal-field strengths and symmetries for Cr3+ dopant i ons. This causes the Huang-Rhys factor of the T-4(2) --> (4)A(2) trans ition to vary from site to site, leading to a strongly broadened lumin escence band. This luminescence is blue-shifted and strongly quenched with increasing temperature, Calculations show that this behaviour is due to large variations in the internal conversion rates for ions in d ifferent parts of the crystal-field distribution. It is shown that a c onfinement potential rather than a harmonic potential is required to a ccount for the data.