Context and Motivation
The research towards the advancement of semiconductor quantum dots (QDs) that are efficient emitters in the near-infrared (NIR) or short-wave infrared (SWIR) region are of paramount importance for NIR-based technologies, including biomedical imaging, telecommunications, night-vision sensors, health monitoring food inspection, and energy-efficient lighting. However, most of the efficient NIR-emitting QDs reported, rely on toxic heavy metals like lead (Pb) and mercury (Hg), which are restricted under the European Restriction of Hazardous Substances (RoHS) directive. This regulatory constraint, combined with growing environmental and health concerns, has created an urgent need for RoHS-compliant, high-performance alternatives that match or surpass the optical properties of Pb/Hg-based QDs.
Existing heavy-metal-free alternatives, such as I-III-VI (e.g. CuInS2, AgInSe2) and III-V (e.g. InAs) QDs, suffer from key limitations:
• Low photoluminescence quantum yield (PLQY) beyond 1000 nm.
• Broad emission linewidths (>150 meV), reducing spectral precision.
• Limited tunability across the SWIR range (1000–1400 nm).
This project, NIRLUMIN, addresses these challenges by developing novel heterostructured QDs based on I-III-VI, Cu-Zn-In-Se (CZISe) with engineered shells (ZnS/Al2O₃) to achieve high efficiency, narrow emission, and environmental stability—while remaining fully RoHS-compliant.
Overall Objectives
The project’s primary goal was to design, synthesize, and optimize heavy-metal-free efficient NIR-emitting QDs as a potential alternative to the Pb/Hg-based QDs. Specific objectives included:
• Synthesis and development of I-III-VI-based QDs via partial cation exchange, enabling precise control over morphology (triangular, spherical, cubic) and size.
• Enhancement of optical properties and stability through core-shell engineering targeting: high PLQY, tunable emission beyond 1000 nm with narrow emission linewidth and long term stability.
• For biocompatibility, encapsulate the core-shell QDs with a ceramic-type shell of alumina (Al2O3) to provide further passivation and prevent degradation of the nanocrystals in different environments as well as the associated leaching out of metal ions, which can have toxic effects (e.g. zinc).
• Surface functionalization for compatibility with optoelectronic devices (LEDs, sensors) and biomedical applications (aqueous dispersion).
• Proof-of-concept integration into NIR-LEDs and down-conversion systems.
