Electronic structure and optical properties of Na₂KSb and NaK₂Sb from first-principles many-body theory

In the search for novel materials vacuum electron sources, multi-alkali antimonides and in particular sodium-potassium-antimonides have been recently regarded as especially promising due to their favorable electronic optical properties. framework of density-functional theory many-body perturbation theory, we investigate structure dielectric response two representative members this family, namely Na$_2$KSb NaK$_2$Sb. We find that both a direct gap, which is on order 1.5 eV 1.0 either system, valence conduction bands are dominated by Sb states with p- s-character, respectively. The imaginary part function, computed upon explicit inclusion electron-hole interactions characterize materials, exhibits maxima starting from near-infrared region, extending up visible ultraviolet band. With our analysis, clarify lowest-energy excitations non-excitonic nature binding energy 100 meV. Our results confirm potential NaK$_2$Sb photoemissive photomultipliers, imaging devices.