Hot Electrons from Consecutive Exciton–Mn Energy Transfer in Mn-Doped Semiconductor Nanocrystals

Abstract

INTRODUCTIONGeneration of hot electrons in metallic or semiconducting materials and hot electron-induced chemistry on their surfaces have been actively investigated for decades. For instance, optically excited hot electrons with excess energy above the Fermi level of metals demonstrated its capability to transfer part of the electron energy to the adsorbate molecules and excite their internal modes initiating various surface chemistries. 1À6 In semiconductors, hot electrons excited above the conduction band edge have been shown to be beneficial in catalysis and photovoltaic applications via fast interfacial charge transfer that can effectively compete with intraband relaxation. 7À9 Recently, a number of groups reported efficient interfacial charge transfer of optically excited hot electrons in semiconductor nanocrystals, 10À12 demonstrating the potential of harvesting hot electrons in nanocrystals that are widely employed in catalysis and photovoltaic applications. Hot electrons with larger excess energy will generally experience a lower energy barrier for interfacial charge transfer, and their wave functions can reach further away from the nanocrystals, making them potentially useful for photocatalytic and photovoltaic applications.Hot electrons in semiconductor nanocrystals can be excited via optical excitation in a number of different ways. The simplest way is the above-band-gap excitation with sufficient excess energy that can excite the electrons high in the conduction band. Hot electrons with higher excess energy generally require excitation with the higher-energy photons in the UV region, which is increasingly less convenient to work with. The lowerenergy photons can also excite hot electrons with large excess energy via multiphoton excitation. 13À15 However, multiphoton excitation is usually much less efficient than single photon excitation and requires high excitation intensity.

Nonplasmonic Hot‐Electron Photocurrents from Mn‐Doped Quantum Dots in Photoelectrochemical Cells

“…Hot electrons with excess energy above the band edge or Fermi level in semiconductors, metals, and their heterostructures have attracted significant attention for their superior electron‐transfer capability compared with lower‐energy counterparts in applications such as photocatalysis or devices . For instance, the ability of hot electrons to enhance or enable the photocatalytic reactions, including H 2 production, water splitting, and dissociation of H 2 , has been demonstrated .…”

“…This work demonstrates the possibility of harvestingh ot electrons not only at the interface of the doped quantum dot surface, but also far away from it, thus taking advantage of the capability of hot electrons for long-range electron transfer across athick energy barrier.Hot electrons with excesse nergy above the band edge or Fermi level in semiconductors, metals, and their heterostructures have attracted significant attention for their superior electron-transfer capability compared with lower-energy counterpartsi na pplicationss uch as photocatalysis or devices. [1][2][3][4][5][6][7][8][9][10] For instance, the ability of hot electrons to enhance or enable the photocatalytic reactions, including H 2 production, [4,11,12] water splitting, [13] and dissociation of H 2 ,h as been demonstrated. [14,15] In photocatalysis, hot electrons are more effective for the reduction reaction, as they not only provide the necessary thermodynamic driving force, especially for the energetically expensive reactions, but also facilitate the transfer of electrons across the barrier between the electron donor and acceptor.…”

Excitation-tailored dual-color emission of manganese(II)-doped perovskite nanocrystals

“…46 Together with Auger recombination in semiconductor NCs 47 and nonradiative cross relaxation in Mn 2þ , 48 the energy-transfer bottleneck may substantially modify the intensity ratio between the band-edge emission and the dopant emission with changing excitation density. Such color-tunable luminescence has been intensively studied for Mn 2þ -doped chalcogenide II-VI semiconductor NCs [46][47][48][49] but remains poorly understood for Mn 2þ -doped perovskite NCs.…”

“…Several mechanisms have been proposed to explain the saturation of dopant emission in conventional Mn 2þ -doped II-VI semiconductor NCs. [46][47][48][49] Besides the initially proposed bottleneck effect for energy transfer from excitons to 4 T 1 states in dopants [ Fig. 3(a)], 46 different types of many-body effects such as multiexciton Auger recombination in NCs [ Fig.…”

Hot Charge Carriers in Quantum Dots: Generation, Relaxation, Extraction, and Applications

“…This excited Mn* can transfer its energy to the electron in CB of QDs via Auger type cross relaxation mechanism resulting in the generation of hot electrons in the QDs. In the alternate mechanism, it was proposed that the energy of exciton can be transferred to the existing|Mn*> creating|M**> which is equivalent to producing a hot electron in the CB of the host and a localized hole at the Mn site as suggested in earlier study by the same group. By this process, absorption of two low energy photons generate a hot charge carrier in QDs which otherwise is not possible.…”