BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d4b3e75f993 DTSTART:20250123T090000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium SUMMARY:ICFO | STEPHY VINCENT CLASS:PUBLIC DESCRIPTION:Shortwave infrared (SWIR) light sources are highly significant due to their ability to interact with molecular bonds and penetrate materi als with reduced scattering and absorption. These properties make SWIR lig ht exceptionally valuable across diverse applications\, including spectros copic analysis\, non-invasive biomedical imaging\, food and agriculture\, and environmental monitoring. However\, traditional SWIR sources tend to b e bulky\, inefficient\, and characterized by high bulb temperatures\, prol onged warm-up times\, limited dimming capabilities\, relatively short life spans\, and high costs. This has resulted in an increasing demand for more efficient\, compact\, and cost-effective alternatives.\nSolution-processe d colloidal quantum dots (CQDs) are promising candidates for advanced SWIR light sources due to their wavelength tunability\, high photoluminescence quantum yield (PLQY)\, and cost-effective synthesis. While CQD-based ligh t sources are well-established in the visible range\, there is a need for further development of SWIR emitters. This thesis addresses this gap by ut ilizing CQDs to create efficient\, flexible SWIR light emitters through a simplified and cost-effective fabrication method.\nWe developed SWIR light emitters with an emission wavelength of around 1350 nm using the down-con version (DC) technique\, where lead sulfide (PbS) quantum dots (QDs) absor b high-energy photons and emit lower-energy SWIR photons. Down-conversion using QDs addresses certain drawbacks of conventional phosphor-converted L EDs based on lanthanides or transition metal ions\, such as the need for c omplex fabrication processes involving high-temperature sintering or annea ling\, limited emission band tunability\, and challenges in supporting pul sed operations. We used binary blends of large-bandgap matrix QDs and smal l-bandgap emitter QDs\, as they are reported to improve the PLQY.\nInitial ly\, flexible DC films were fabricated on PET substrates via solid-state l igand exchange (SSLE) and spin coating\, with various ligands\, including 3-Mercaptopropionic Acid (MPA)\, combinations of Zinc Iodide (ZnI2) and MP A\, and combinations of 1-Ethyl-3-methylimidazolium Iodide (EMII) and MPA\ , studied. The best performance was achieved using MPA as the ligand\, and selectively exciting the emitter QDs proved more efficient than exciting both matrix and emitter QDs. The DC film treated with MPA\, when excited b y a 980 nm LED produced a SWIR power density of 0.19 mW mm⁻²\;. Desp ite these promising results\, spin coating was found to be inefficient and labor-intensive\, necessitating a more scalable method.\nTo address this\ , we developed an alternative fabrication method using ethyl cellulose (EC ) polymer\, where oleic acid-capped QDs are mixed with EC to form flexible QD-EC composites. This approach is industrially adaptable\, reduces QD us age by a factor of 20\, eliminates wastage\, and requires less manual effo rt than the SSLE process. It also allows for scalable fabrication of DC fi lms in any size or shape. The maximum SWIR power density achieved for a DC film with OA-capped PbS QDs\, without ligand modification\, was 0.18 mW m m⁻²\; .\nTo further enhance efficiency\, we applied solution-phase l igand exchange (SPLE) using 1-dodecanethiol (DDthiol) to improve surface p assivation and reduce non-radiative recombination. DC films made with DDth iol-treated PbS QDs demonstrated a three-fold increase in SWIR power outpu t and reduced efficiency roll-off by 37% at higher excitation power\, comp ared to films with oleic acid (OA)-capped QDs. The best-performing film\, composed of DDthiol-treated matrix QDs and OA-capped emitter QDs\, achieve d a maximum SWIR power density of 0.54 mW mm⁻²\; . This methodology was further extended to develop SWIR light sources emitting at 1470 nm. In summary\, we developed efficient and flexible SWIR light sources using so lution-processed CQDs through a cost-effective and scalable fabrication me thod by overcoming the limitations of conventional sources.\n \;\nThur sday January 23\, 10:00 h. ICFO Auditorium \nThesis Director: Prof. Dr. Ge rasimos Konstantatos DTSTAMP:20260407T073607Z END:VEVENT END:VCALENDAR