Photodarkening experiments are performed on ytterbium-doped silicate glass
samples. A strong charge-transfer (CT) absorption band near 230nm in
aluminosilicate glass is found to be correlated to the mechanism of induced
color center formation. Excitation into the CT-absorption band generates
similar color centers as observed in ytterbium-doped fiber lasers under
915nm high power diode pumping. The position of the CT-absorption band is
compositional dependent and is shifted to shorter wavelengths in ytterbium
doped phosphosilicate glass. Very low levels of photodarkening is observed
for the ytterbium doped phosphosilicate glass composition under 915nm high
power diode pumping. Possible excitation routes to reach the CT-absorption
band under 915nm pumping are discussed.