  We experimentally demonstrate optical bistability in Er3+-Yb3+ phosphate
glass microspheres at 295 K. Bistability is associated with both Er3+
fluorescence and lasing behavior, and chromatic switching. The chromatic
switching results from an intrinsic mechanism exploiting the thermal coupling
of closely-spaced energy levels, and occurs simultaneously with the intensity
switching. A contrast ratio of 3.2 has been obtained for chromatic switching,
and the intensity switching shows ratios of 2.4 for 550 nm and, 1.8 for the 660
nm fluorescence emissions, and 11 for the IR lasing at 1.5 um. Concurrent with
these observations, we investigate a temperature dependent absorption of pump
power which exhibits bistable behavior. The influences of the host matrix on
lasing and fluorescence mechanisms are highlighted.
