We investigate the spontaneous emission of a single quantum emitter coupled to quasibound states in the continuum (QBICs) supported by dielectric gratings. Using quasinormal mode theory, we calculate the radiative enhancement induced by both regular and dimer grating structures. This approach allows us to determine the optimal dimer grating and to study the impact of structural disorder on these structures. We show that structural disorder can convert symmetry-protected bound states in the continuum in regular gratings into QBICs, opening radiative channels at normal incidence. Through statistical simulations, we identify the respective roles of dimensional and positional disorder. Finally, we show that dimer gratings retain high radiative efficiency for moderate disorder strengths below $10\%$. Beyond this threshold, both structures exhibit comparable efficiencies.

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• Bound states in the continuum
• Photonics
• Spontaneous emission