Optical Transparency Enabled by Anomalous Stokes Shift in Visible Light-Emitting CuAlS2-Based Quantum Dots
Biswajit Bhattacharyya1, Triloki Pandit1, Guru Pratheep Rajasekar1
1Solid State and Structural Chemistry Unit , Indian Institute of Science , Bangalore 560012 , India.
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.
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