Biexciton cascade emission reveals absolute absorption cross section of single semiconductor nanocrystals

The sequential two-photon emission process known as biexciton cascade emission is a characteristic phenomenon that occurs in photoexcited semiconductor nanocrystals (NCs). This process occurs when a biexciton state is created in the NCs; thus, the occurrence of the process is related to the photoabsorption properties of the NCs. This paper presents a simple equation that connects the photoabsorption of single NCs and the biexciton cascade emission. The equation is found to be independent of the quantum yields of photoluminescence (PL). With this equation and using an analysis of second-order photon correlation, the absolute absorption cross section sigma of the single NCs can be evaluated, obtaining values on the order of 10(-14) cm(2). This analysis shows that ionization during PL blinking does not affect the validity of the relation, indicating that the evaluation of sigma, based on the equation, is applicable for various NCs with unique structures.