SIZE-DEPENDENT SPECTROSCOPY OF INP QUANTUM DOTS

The spectroscopic behavior of colloidal InP quantum dots (QDs) has bee n investigated as a function of the mean QD diameter (which ranged fro m 26 to 60 Angstrom). Absorption spectra show up to three peaks or sho ulders which reflect excited state transitions in the QDs. Global phot oluminescence (PL) spectra (excitation well to the blue of the absorpt ion onset and which consequently excites most of the QDs in the size d istribution) show broad PL emission. The emission and absorption featu res shift to higher energy with decreasing QD size. Resonant PL spectr a (size-selective excitation into the tail of the absorption onset) sh ow increasing fluorescence line narrowing with increasing excitation w avelength PL and photoluminescence excitation spectroscopy were used t o derive the PL red shift as a function of QD size. The resonant red s hifts for QDs of a single size were extracted from PL data that reflec t the emission from an ensemble of QD diameters. An analysis of the si ngle-dot resonant red shift (difference between PL peak and the first absorption peak) as a function of the single QD diameter indicate that the results are consistent with a model in which the emission occurs from an intrinsic, spin-forbidden state, split from its singlet counte rpart, due to screened electron-hole exchange.