HgCdSe/HgS/CdZnS Colloidal Quantum Wells with Bright Short-Wave Infrared Light Emission

Abstract

There has been a growing interest in bright short-wave infrared (SWIR; 1000-1700 nm) light emitters for their unique applications in biomedical imaging and optoelectronics. Previous studies have shown that core/shell quantum dots (QDs) such as PbS/CdS/ZnS and InAs/CdSe/CdS can emit bright, stable, and wavelength-tunable SWIR lights. However, these QDs showed high QYs (up to 80%) only in a part of SWIR window (1000-1100 nm) and in organic solution, otherwise QYs dropped significantly (lower than 30%). To address these limitations, we engineered a new SWIR nano-emitter by synthesizing CdHgSe/HgS/CdZnS colloidal quantum wells (QWs), which can exhibit bright emission across the whole SWIR region in both organic solution and water. Our SWIR QWs were synthesized via multi-step colloidal reactions to (1) prepare CdHgSe core via a partial Cd-to-Hg cation exchange on CdSe QD surface, (2) grow HgS emitting layer with controlled thickness over CdHgSe core to tune the SWIR wavelength, and (3) add CdZnS passivating layer to enhance QY and photostability (Figure 1a). Photoluminescence (PL) measurements showed that our SWIR QWs can emit bright, narrow (FWHM 150-300 nm) SWIR emission tuned between 1050 to 1550 nm. Moreover, absolute photoluminescence QY measurements confirmed that our SWIR QWs can exhibit much higher QYs than previous QDs in both organic solution and in water after encapsulating with amphiphilic polymer (Figure 1b). Furthermore, we could make bright AC-driven SWIR LEDs covering full SWIR spectrum operating at much lower threshold voltage than visible ones by using our SWIR QWs. We expect that our SWIR QWs would find various future applications including bright SWIR probes for deep tissue biomolecular imaging and non-invasive medical imaging and active layers for flexible SWIR LEDs.