| dc.description.abstract | Hot charge carrier generation and extraction from semiconducting and metal nanoparticle materials have been heavily researched from their potential to preform chemistry that regular electrons are not capable of. One major hurdle that inhibits the practical use of hot electrons is the need for high energy photons or high photon fluxes for their generation in most semiconductors, which is not readily available through solar radiation. Noble metal nanoparticles are able to generate hot electrons under visible radiation but due to the low relative energy of the hot electrons their use for jumping over energetic barriers and photocatalysis is limited.
Colloidal semiconductor nanocrystals have been at the forefront of nanoscience research from the wide range of interesting properties that are imparted on them from quantum confinement effects that result in new physical processes when compared to their bulk counterparts. The promising optical properties of these materials with high quantum yields and photostability has made them useful in biological, photovoltaic, photocatalytic, and optoelectronic applications. In 3-dimensional confined quantum dots, the excitonic wavefunction can extend throughout the volume of the structure yielding greater sensitivity to the addition of dopants, further increasing the ability to manipulate the optical properties.
Doping Mn in II-VI quantum dots has been of interest from the many optical and magnetic properties that it imparts on the host structure. The ⁴T₁ – ⁶A₁ transition has a low probability to occur from its small cross section due to its spin forbidden nature, relying on energy transfer from the host structure. The forbidden nature of this transition results in long millisecond photoluminescence lifetimes. The long lifetime of the Mn excited state is able to facilitate hot electron generation under low intensity cw excitation via two photon upconversion. This process occurs as follows: the first photon creates an exciton that has energy transfer to the Mn followed by another exciton being formed which the Mn undergoes back energy transfer excited state electron 2 eV further into the conduction band. The hot electrons generated in this have the ability to outcompete regular electrons in photocatalysis, the ability to be photoemitted from the quantum dot, and pass through an insulating barrier. While these results show the capability of hot electrons, the hot electron generation efficiency is still low which creates the need to explore new material systems that have higher inherent quantum yields to better facilitate this process.
To circumvent this issue, cesium lead halide perovskite nanocrystals, which have photoluminescence quantum yields near unity, were explored as new material system for hot electron generation. The synthetic background for Mn doping in CsPbCl₃ and CsPbBr₃ was developed which will allow for the verification and study of the hot electron generation for this material. A new photoinduced anion exchange method was also developed which can allow for greater tunability of the perovskite optical properties. To further push the boundaries and capabilities of hot electrons, the photocatalytic reduction of CO₂ was studied using a hybrid quantum dot/metal catalyst system that showed the long-range electron transfer to the catalyst from the quantum dot via hot electrons. | en |
