Photon bunching in cathodoluminescence.

We have measured the second order correlation function [g^{(2)}(τ)] 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)}(τ) 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)}(τ) 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.