Excitons in CsPbX3 (X=Cl, Br, I) ternary nanocrystallites in thin film matrices

Ternary nanophases based on Cs–Pb–X (X=Br, Cl, I) composition, were evidenced in polycrystalline thin films grown by physical vapour deposition. Optical properties of these nanostructures were determined by absorption, emission and decay kinetics measurements. Nanocrystals of CsPbX3 type were found to be in agreement with reported band-structure calculations (X=Cl, Br); they show optical features of a wide band-gap semiconductor with direct band-to-band transitions. Ternary bromide and chloride phases show, at 10 K, a pronounced fast free Wannier exciton emission (leading decay time <1 ns) peaking round 537 and 420 nm, respectively, with very small Stokes-shift. On the contrary, the nanophase of CsPbI3 is characterised by the auto-localised exciton emission around 535 nm, longer decay times in μs time scale and a pronounced Stokes-shift. In all the cases, the optical features are closely similar to the ones of the bulk ternary crystals, which were reported earlier.