Exploring magneto-optic properties of colloidal two-dimensional copper-doped CdSe nanoplatelets

Abstract

Transition-metal-doped semiconductor nanocrystals have received significant attention because of their attractive features deeming them invaluable in various technological fields including optoelectronics, bio-photonics, and energy conversion, to name a few. Of particular, these interests are two-dimensional materials with useful optical and magnetic properties combined with their large surface areas opening up new applications in biotechnology. These applications range from multimodal optical and magnetic bioimaging and sensing to measuring the weak magnetic field due to brain waves using their magneto-optic properties stemming from the exchange interaction between the transition metal dopants and the carrier spins. These magnetic 2D materials could also significantly advance the field of spintronics. In this work, we report on a study of the magnetic and magneto-optic properties of colloidal two-dimensional (2D) copper-doped CdSe nanoplatelets (NPLs) that are synthesized using a high-temperature colloidal technique. We carried out optical and circularly polarized magneto-photoluminescence spectrometry to investigate the magnetism in our solution-processed nanostructures doped with copper ion impurities. At cryogenic temperatures, two excitonic features are observed for doped NPLs, which are more prominent compared to the undoped NPLs. Furthermore, the excitonic circular polarization (CP) is recorded as a function of the applied magnetic field (B) and temperature (T). The detailed analysis provides a picture of the magneto-optical behavior of the doped 2D NPLs in the presence of paramagnetic copper ions. This work paves the way for significant advances in bio/nanophotonics where tunable optical and magnetic properties of doped nanoplatelets can be leveraged to make more efficient, flexible, and low-cost devices.

Possibility of Exciton Bose–Einstein Condensation in CdSe Nanoplatelets

“…When the weak nonideality of a two-dimensional exciton gas is considered, the specificity of two-dimensional scattering at low energies manifests itself due the fact that the scattering amplitude (also the scattering cross-section) increases with decreasing energy of the scattering particles. In this case, parameter (23) or an equivalent parameter:…”

“…From expressions (23) and (31), it is clear that if, at some value of the quasi-wave vector K (or energy) of the scattering particles, a control measurement of the value of the scattering cross-section is carried out, then, according to expressions (23) and (31), it is possible to determine the value of the cross-section already at any energy values that satisfy the above requirements for low energies.…”

“…In particular, the giant oscillator strength, narrow emission, large absorption cross-section, sizeable optical gain, and a much higher binding energy of a two-dimensional exciton as was illustrated compared to a case involving quantum film that had been observed in NPLs [1,4,5,[17][18][19][20]. Therefore, semiconductor NPLs are very promising materials that can be used to create several optoelectronic devices: light emitter devices of various ranges, light generation and amplification devices [12,16], lasers [16][17][18], solar energy harvesting applications [19,20], photodetectors [21][22][23][24], photosensors [22][23][24], etc. Note that the exceptional fluorescent properties of NPLs make them promising nanomaterials for use in biological and medical applications [9,25,26].…”

“…is the energy spectrum of elementary excitations of the exciton condensate. As we can see, the spectrum of elementary excitations is determined by the momentum of the translational motion of particles and their density in the NPL plane, as well as by the dimensionless two-dimensional scattering parameter from (23).…”

“…Note that the exceptional fluorescent properties of NPLs make them promising nanomaterials for use in biological and medical applications [9,25,26]. NPLs based on II-VI compounds (CdS, CdSe, CdTe [1][2][3][4][5][6][7][8][9][10][11][12][16][17][18][19][20][21][22][23][24][25][26][27][28], HgS, HgSe, HgTe [29][30][31]) and, in part, on IV-VI compounds (PbS, PbSe, PbTe [32,33]) are actively investigated. In what follows, our attention will be focused on NPLs of CdSe.…”