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DTSTART:20260710T080000Z
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LOCATION:ICFO Auditorium
SUMMARY:ICFO | MIGUEL DOSIL GARCÍA
CLASS:PUBLIC
DESCRIPTION:Colloidal quantum dots (CQDs) have established themselves as a 
 key technology in optoelectronics due to their high efficiency\, versatili
 ty\, and low manufacturing costs. Their application in light generation ha
 s evolved from statistical thermal emission in visible LEDs and fluorescen
 ce converters toward more sophisticated sources\, such as lasers and quant
 um light emitters. However\, their implementation in the infrared (IR) has
  proven more complex due to an inherently low photoluminescence quantum yi
 eld (PLQY)\, with efficient applications emerging only recently. Given the
  growing interest in quantum technologies\, single photons in the infrared
  telecommunications C-band have become a fundamental pillar\, a domain whe
 re these colloidal technologies offer superior flexibility. Specfifically\
 , CQDs based on Pb chalcogenides and III-V semiconductor alloys bridge the
  gap between cost and integration thanks to the tunability of their emissi
 on properties within this spectral region. This work presents an optical s
 pectroscopy characterization of PbS and InSb CQD dispersions and films\, e
 mploying steady-state and time-resolved micro-photoluminescence (u-PL) tec
 hniques at low temperatures. To this end\, the complete design and impleme
 ntation of the utilized optical system are detailed\, including alignment 
 and optimization protocols\, as well as the algorithms developed for perfo
 rming confocal u-PL mapping with micrometric resolution. Power-dependent P
 L studies on PbS films reveal a collective behavior characterized by a bim
 olecular recombination regime within a band with an exponential-type densi
 ty of states (DOS)\, which contrasts with the excitonic behavior observed 
 in solution. Furthermore\, the PLQY of these samples shows a marked linear
  dependence on size\, reaching a maximum of ~30\\% for quantum dots with e
 xcitonic peaks around 1.5 eV and steadily decreasing toward larger particl
 es. Time-resolved PL measurements indicate the existence of energy transfe
 r mechanisms between CQDs with long diffusion times. Encapsulation tests c
 onfirm that oxygen acts as a highly degrading agent\, quenching emission a
 fter moderate exposure to ambient conditions. InSb CQDs exhibit extreme se
 nsitivity to oxidation\, losing their PL within seconds upon contact with 
 air. Temperature-dependent PL measurements further reveal the presence of 
 a surface-associated emission band at cryogenic temperatures\, which rapid
 ly disappears upon heating the sample or adding a thin InP shell. Two stra
 tegies were explored to reach the single-particle regime. In contrast to t
 he common use of spin-coating\, dip-coating of dilute solutions proved eff
 ective for obtaining isolated CQDs with controlled areal density\, albeit 
 at the cost of significant luminescence degradation\; this suggests irreve
 rsible damage to the crystal surface due to ligand stripping subsequently 
 oxidating the surface. As an alternative for protecting particles from ext
 ernal agents\, PbS CQDs were encapsulated in thick silica shells using a m
 icroemulsion method in combination with surface chemistry engineering\, su
 ccesfully allowing a high yield of single CQD to silica particle. The resu
 lts presented in this thesis highlight critical limitations in the current
  implementation of IR-emitting CQDs as quantum light sources\, underlining
  the need to develop new synthesis routes and coating chemistries to impro
 ve their optical properties and ensure long-term stability. Additionally\,
  the experiments conducted on films provide relevant perspectives for the 
 optimization of technologies based on infrared CQDs\, such as LEDs\, photo
 detectors\, or lasers.\nThesis Director: Prof. Dr. Gerasimos Konstantatos
DTSTAMP:20260703T034947Z
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