Saturation effects of cathodoluminescence in rare-earth activated epitaxial Y3Al5O12 layers

The intensity of luminescence in YAG, activated with rare-earth ions, shows a nonlinear behavior as a function of incident current density under electron bombardment. Tb3+ or Eu3+ activated samples exhibit deviation from linearity at input power densities exceeding 104 W/m2, while Ce3+ luminescence is linear up to the highest power densities studied (108 W/m2). It is shown that nonlinearity effects, in cases where temperature quenching can be excluded, are caused by saturation of the excited-state population. The results are interpreted in a model which also takes into account excited-state absorption within one activator and energy transfer between neighboring activator ions.