Observation of photoluminescence from Franckeite, a natural van der Waals heterostructure

Van der Waals heterostructures (vdWH) comprised of two-dimensional (2D) materials offer a platform to obtain materials by design with unique electronic properties. Franckeite (Fr) is a naturally occurring vdWH comprised of two distinct alternately stacked semiconducting layers; (i) SnS₀ layer, also known as H layer, and (ii) Pb₃SbS₄ also known as Q layers. Though both H and Q layers in the heterostructure are semiconductors, the photoluminescence from Fracnkeite remains elusive. In this work, we report the observation of photoluminescence (PL) from Franckeite at cryogenic temperature. The PL peak appears at 2.1 eV measured at 1.5 K. We measured PL at varying temperature from 1.5 K to 80 K. We found that both the PL peak and the integrated intensity does not depend on the temperature in the range of 1.5 K to 80 K. We have observed linear dependence of PL integrated intensity on laser power. Our study provides a fundamental understanding of the optical behavior in a complex naturally occurring vdWH and may pave an avenue toward developing nanoscale optical and optoelectronic devices with tailored properties.