| dc.description.abstract | Cesium lead tribromide nanocrystals have remarkably high photoluminescence quantum yield due, in part, to their tolerance to the formation of defect states. Further, the most commonly formed defect—excess lead on the nanocrystal surface—can be removed via a facile treatment, increasing their photoluminescence quantum yield to approximately unity. Their efficient fluorescence makes cesium lead tribromide nanocrystals a promising target for luminescence up-conversion, a phenomenon whereby photons with lower energy and are converted into emitted photons with higher energy. This optical process has applications in bioimaging, as well as optical energy conversion where up-conversion can be utilized to decrease band-gap and thermalization losses. Here, I discuss the development and study of cesium lead tribromide nanocrystals for luminescence up-conversion.
One method for luminescence up-conversion is so-called hot-electron up-conversion. This mechanism utilizes the hot electrons generated in a metal to drive photoluminescence in a semiconductor, a process that is impeded by the quenching of the semiconductor photoluminescence that is typically observed in metal-semiconductor heterostructures. I demonstrate a method for depositing gold nanocrystals onto the surface of CsPbBr3 nanocrystals, as well as discuss the competing reaction pathway that leads to gold cation exchange with lead in the nanocrystal lattice. I demonstrate that CsPbBr3 maintains high efficiency photoluminescence with gold nanoparticles deposited on its surface.
Another up-conversion mechanism to which CsPbBr3 can be applied is one photon up-conversion, also known as anti-Stokes photoluminescence (ASPL). This up-conversion mechanism uses thermal energy from the material to drive up-conversion. If this occurs with efficiency near unity, ASPL depopulates the material’s phonon modes leading to a net decrease in temperature. I demonstrate that efficient CsPbBr3 ASPL does not rely on mid-gap electronic states to act as intermediates. CsPbBr3 ASPL is shown to cool the local environment of the nanocrystals by as much as 25 degrees, using the Raman scattering of a silicon substrate as a reporter for the temperature. Additionally, the thermal scavenging potential of CsPbBr3 ASPL is shown to be enhanced through coupling to a plasmonic substrate, with a greatly enhanced ASPL photon yield as well as more thermal energy removed from the system per up-converted photon. | en |
