Optical Transparency Enabled by Anomalous Stokes Shift in Visible Light-Emitting CuAlS₂-Based Quantum Dots

Abstract

We observe and study the anomalous Stokes shift of CuAlS₂/CdS quantum dots. While all known I-III-VI₂ semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS₂/CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS₂/CdS quantum dots are thus associated with cross sections less than 10^-17 cm² under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS₂ and CdS layers. Besides their strong Stokes shift, CuAlS₂/CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS₂/CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm².