Photon Bunching in Cathodoluminescence

We have measured the second order correlation function [g((2))(tau)] of the cathodoluminescence intensity resulting from the excitation by fast electrons of defect centers in wide band-gap semiconductor nanocrystals of diamond and hexagonal boron nitride. We show that the cathodoluminescence second order correlation function g((2))(tau) of multiple defect centers is dominated by a large, nanosecond zero-delay bunching (g((2))(0) > 30), in stark contrast to their flat photoluminescence g((2))(tau) function. We have developed a model showing that this bunching can be attributed to the synchronized emission from several defect centers excited by the same electron through the deexcitation of a bulk plasmon into few electron-hole pairs.