Nonlinear optical properties of quantum-confined cdse microcrystallites

Quantum-confinement effects in CdSe microcrystallites in a glass matrix are investigated in the nanosecond time domain. The results of pump-probe and single-beam absorption saturation measurements show strong evidence for electron-hole quantization in the semiconductor microstructures, a different bleaching behavior from those of bulk semiconductors and multiple quantum wells, and a trend of increased saturation intensity with decreased microcrystallite size. A theory for the one- and two-pair states in quantum dots is developed that fully includes the relevant Coulomb interactions. The theory is evaluated numerically, and results are presented for intrinsic quantum dots and for quantum dots with impurities. The experimentally observed nonlinearities are attributed to saturation of one-electron-hole-pair resonances and induced absorption caused by two-pair resonances in the presence or absence of impurities (traps).