  We study the effect of coupled resonances and quasi-bound states in the
continuum (quasi-BICs) on the Purcell factor in dielectric resonant
nanoantennas. We analyze numerically interfering resonances in a nanodisk with
and without a substrate when the modes are coupled to an emitter localized
inside the nanodisk, and we quantify the modal contributions to the Purcell
factor also reconstructing the radiation patterns of the resonant system. It is
revealed that the Purcell effect can be boosted substantially for a strong
coupling of resonances in the quasi-BIC regime.
