AgInS2-ZnS nanocrystals: Evidence of bistable states using light-induced electron paramagnetic resonance and photoluminescence

The precursor (AgIn)x Zn2(1–x)(S2CN(C2H5)2)4 was used to prepared AgInS2–ZnS nanocrystals with different compositions (x = 0.4 and x = 0.7) and with different time of reaction (10 min and 75 min). The photoluminescence features of the nanocrystals were addressed by combining steady‐state spectroscopy and light‐induced electron paramagnetic resonance. Both techniques showed the contribution of at least two components for the emission, previously assigned to surface and intrinsic states. Light‐induced electron paramagnetic resonance allowed detection of the photocreation both of irreversible paramagnetic species that are likely responsible for the nano‐crystals degradation assigned to surface states and of reversible paramagnetic species assigned to intrinsic states. Moreover, reversible bistable paramagnetic states were observed. This Letter provides a scheme that might be useful in addressing the well‐known problem of aging of the nanocrystals. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Electron paramagnetic resonance (EPR) and photoluminescence (PL) of AgInS2–ZnS nanocrystals reveal at least two kinds of photoinduced defects: one is irreversible and assigned to surface states while the other one is fully reversible and attributed to core states. EPR allows detection of a bistable paramagnetic species. Such discrimination between irreversible and reversible phenomena allows addressing the crucial aging problem of quaternary nanocrystals.