Excitonic pathway to photoinduced magnetism in colloidal nanocrystals with nonmagnetic dopants

Abstract

Electronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Ag is an emerging electronic dopant in III-V and II-VI nanostructures, introducing intragap electronic states optically coupled to the host conduction band. With its full 4d shell Ag is nonmagnetic, and the dopant-related luminescence is ascribed to decay of the conduction-band electron following transfer of the photoexcited hole to Ag. This optical activation process and the associated modification of the electronic configuration of Ag remain unclear. Here, we trace a comprehensive picture of the excitonic process in Ag-doped CdSe nanocrystals and demonstrate that, in contrast to expectations, capture of the photohole leads to conversion of Ag to paramagnetic Ag. The process of exciton recombination is thus inextricably tied to photoinduced magnetism. Accordingly, we observe strong optically activated magnetism and diluted magnetic semiconductor behaviour, demonstrating that optically switchable magnetic nanomaterials can be obtained by exploiting excitonic processes involving nonmagnetic impurities.

Magnetic Circular Dichroism in Nanomaterials: New Opportunity in Understanding and Modulation of Excitonic and Plasmonic Resonances

“…Since early 1990s, MCD technique has found its efficiency in direct measurement of excited state Zeeman splitting, [68][69][70][71] which is the basis for determination of the g-factor of excitons in semiconductor nanocrystals [72][73][74][75] and demonstration of the sp-d exchange interactions in diluted magnetic semiconductor nanocrystals. [34,[76][77][78][79][80][81] Very recently, MCD has displayed its new opportunities in analyzing fine structure in semiconductor nanoclusters. [81][82][83]…”

Blue Light Emitting Defective Nanocrystals Composed of Earth‐Abundant Elements

“…In general, intra‐band gap states can be introduced into NCs by incorporation of either intrinsic or extrinsic dopants. Extrinsic doping of NCs has been shown to result in efficient PL with large Stokes shift via incorporation of dilute quantities of Cu + , Ag + , Mn 2+ , and other metal ions . However, extrinsic dopant‐containing NCs necessarily require a host crystal matrix, which has historically been Cd‐ or Pb‐based, thereby presenting toxicity issues.…”

Quantized Electronic Doping towards Atomically Controlled “Charge-Engineered” Semiconductor Nanocrystals

“…Charge engineering of p-and n-type bulk semiconductors through the insertion of heterovalent atoms with respect to the host lattice, commonly referred to as 'electronic impurity doping', is standard practice and arguably the most powerful material engineering paradigm underpinning contemporary microelectronics. Its extension to NCs synthesized directly in the liquid phase, aided by the enhanced interaction between the impurity charges and the spatially-confined carriers, would unlock fundamental properties that cannot be achieved with other motifs, such as unidirectional emissiononly photophysics [12][13][14] , enhanced charge mobility [15][16][17][18] and photo-controlled magnetic behaviours 19,20 .…”