Linear Absorption and Molar Extinction Coefficients in Direct Semiconductor Quantum Dots

We present a simple theoretical analysis of the linear absorption coefficient due to interband transition in quantum dots of direct bandgap semiconductor materials aimed at quantification of the quantum dot concentration in colloidal suspensions. We establish the relationship of the linear absorption coefficient thus calculated with the universally used molar extinction coefficient to be able to compare our theoretical predictions with experimental studies. On the basis of this foundation, we develop a simple approach to calculate the value of the coefficient using empirical values taken from the extinction measurements and basic physical parameter of materials. We explain the long-standing discrepancies between the theories of quantum dot absorption and experiments as well as the trends of the extinction coefficient with varying quantum dot size.