Hole doping in correlated CT — insulators: LixNi1−xO

Experimental results on the optical absorption in Li doped NiO are presented. Upon Li doping, considerable oscillator strength is found to appear throughout the fundamental absorption gap until at 2% doping the d-d excitations usually observed within the gap are completely overwhelmed by these new excitations. Low energy REELS measurements on the same set of samples do not show the same behaviour. We briefly discuss the compatibility of our findings with results of previous electron spectroscopic results and with theoretical scenarios.