Title: Colloidal Quantum Dots and Carbon Dots for Optical Gain and Tunable Photoluminescence
Research Supervisor: Dr. Asha Bhardwaj
Mode: Online
Abstract:
Optical fiber amplifiers underpin modern photonics, but those based on rare-earth ions are limited in bandwidth by the discrete transitions of the dopant. This thesis explores nanocrystal gain media, colloidal quantum dots and carbon dots, as alternatives whose emission can be tuned by design, and asks what limits their gain and how to engineer around it.
For quantum dots, we show that alloyed Cd₁₋ₓZnₓSe/ZnSe core–shell dots, in which Auger recombination is suppressed, sustain continuous-wave amplified spontaneous emission at room temperature, with a threshold of 31 W cm⁻². We transfer this gain into a hollow-core fiber using anisotropic CdSe/CdS and CdZnSe/CdSe/ZnS dots and then address reabsorption and low emission efficiency with a large-Stokes-shift dot design and a self-assembled silver-nanoparticle micro neck structure, which gives a 5.1-fold emission enhancement.
For carbon dots, we turn to a metal-free platform. Protonation-assisted surface functionalization produces red-emitting carbon dots with a photoluminescence quantum yield of 96.4%. Through FTIR, XPS, NMR, zeta-potential and solvent-dependent measurements, we show that the emission depends on both the protonation state of surface amine groups and the dispersion of the particles. Loaded into a hollow-core fiber, these dots amplify an injected signal over a bandwidth of about 80–90 nm. A second surface-engineering route gives bright, tunable white emission in both liquid and solid states.
Together, these results link nanocrystal surface and structure engineering to device-level performance in fiber-integrated gain and LED emission.
Please find the meeting link:
https://teams.microsoft.com/l/meetup-join/19%3ameeting_ZjQwOWFiNjMtODI4ZS00YmViLWEwNWQtZTZmNjY4OTdhODU3%40thread.v2/0?context=%7b%22Tid%22%3a%226f15cd97-f6a7-41e3-b2c5-ad4193976476%22%2c%22Oid%22%3a%22c095b68c-edc5-4f8a-b2e3-2172b02b290b%22%7d
Refreshments will be served after the Colloquium.
ALL ARE WELCOME.