Near‐Infrared‐Emitting Five‐Monolayer Thick Copper‐Doped CdSe Nanoplatelets

Abstract

Copper doping in the semiconductor nanocrystals (NCs) has been fascinating much attention nowadays, which offers high performance in a variety of optoelectronic applications. [1][2][3][4] In the last two decades lots of work has been done on doping of Cu in NCs of different materials, e.g., ZnSe, ZnS, CuInS, and CdSe. [2,[4][5][6][7][8][9][10][11] Doping of Cu(I) typically creates a midband-gap state in the band gap of the host semiconductor NCs, which captures the photoexcited holes and thus allows a radiative recombination of photogenerated electrons in the conduction band. [2,12,13] These doped NCs possess a broadband and tunable visible to near-infrared (NIR) dopant induced emission, nearly zero self-absorption, high photoluminescence (PL) quantum yield (QY), and p-type conductivity, which make these NCs one of the promising candidates for their possible use in luminescent solar concentrators (LSCs), light-emitting diodes, color conversion devices, lasers, and optical fibers. [1][2][3][14][15][16] Recently Gamelin et al. studied different NC phosphors for their possible application as LSC emitters. [1] This study demonstrates Cu-doped CdSe quantum dots (QDs) as the most suitable material for LSCs as compared to widely studied Mndoped ZnCdS/ZnS QDs, CdSe/CdS dots in rods, and CdSe/ CdS giant QDs. Cu-doped CdSe QDs possess moderate PL QYs (20%-30%), large Stokes shift, NIR emission, and higher absorption overlap with the solar spectrum, which altogether boosts their performance in LSCs. Very recently, Cu-doped three to four monolayer (ML) CdSe nanoplatelets (NPLs) were added into the family of colloidal quantum wells that possess extraordinarily high PL QYs (80%-90%), large Stokes-shifted NIR emission, high absorption cross-sections, and step-like optical absorption profiles. [15] As compared to colloidal QDs, CdSe NPLs by exploiting the atomically precise and identical thicknesses effectively eliminate the inhomogeneous broadening of the absorption and emission spectra. [17,18] This also leads to ideal step-like absorption profiles. These extraordinary properties allow the doped NPLs to find use for solar light harvesting applications. [15] However, for further improvement in the performance of these doped NPLs as LSC materials, their Doped nanocrystals are instrumental to the high-performance luminescent solar concentrators (LSCs) and the color conversion devices. Recently, copper (Cu)-doped three and four monolayer (ML) thick CdSe nanoplatelets (NPLs) have been shown superior to the existing Cu-doped quantum dots (QDs) for their use in LSCs. However, additional improvement in the LSC performance can be achieved by further redshifting the emission into the near-infrared (NIR) region of electromagnetic spectrum and increasing the absorbed portion of the solar irradiation. Cu-doping into higher thicknesses of these atomically flat NPLs (e.g., ≥5 ML) can achieve these overarching goals. However, addition of the dopant ions during the nucleation stage disturbs this high-temperature growth process and leads to mul...

Manipulation of the Optical Properties of Colloidal 2D CdSe Nanoplatelets

“…[ 22 ] By changing the thickness from 3‐ML to 5‐ML, Cu + cation–related PL redshifts due to the relaxation of quantum confinements of electrons in CdSe host materials. [ 100 ] Regarding the tunability of Cu impurity emission, another way to change the quantum confinement for the host system is to dope Cu ions into CdSe‐based heterostructures. Bicolor PL and absorption spectra of Cu‐doped CdSe/CdS core/shell NPLs prepared by c‐ALD techniques at room temperature are displayed in Figure 5b.…”

“…[ 97 ] However, in comparison to these Cu‐doped CdSe QDs, Cu‐doped CdSe NPLs exhibit PLQY higher than 65% and larger Stokes‐shifted emission in the NIR regime. [ 100 ] As displayed in Figure 5f, Cu‐doped CdSe NPLs are sandwiched between two glass substrates. Upon illumination with a high‐energy optical source, the light in the NPL region is waveguided through total internal reflection and is eventually emitted at the edges.…”

Temperature-Dependent Photoluminescent Properties of PbSe Nanoplatelets

“…Since that time, PbS [ 10 , 11 , 12 , 13 , 14 , 15 ], PbSe [ 16 , 17 ], PbSe 1− x S x [ 18 ], and HgTe [ 19 , 20 ] NIR-emitting NPLs were synthesized using both oriented attachment and cation exchange procedures. A different strategy to obtain NIR-emitting NPLs was to dope visible-emitting CdSe NPLs with Ag [ 21 , 22 ] or Cu [ 23 ]. Curiously, that HgTe NIR-emitting NPLs exhibit optical properties typical for this class of objects, including narrow PL width and short PL lifetimes.…”

Light-Induced Paramagnetism in Colloidal Ag+-Doped CdSe Nanoplatelets

“…In II–VI semiconductors, Mn is an isovalent impurity and therefore cannot introduce excess carriers to the system, which is important for optoelectronic applications. In contrast, Cu and Ag dopants in II–VI semiconductor NCs act as acceptors that can capture photoexcited holes from the VB. − The incorporation of Cu + and Ag + ions creates an acceptor state above the top of the host VB. Transitions between the CB and the impurity state are responsible for the bright phosphor emission in these materials. ,− Recent density functional theory calculations by Nelson et al indicate that in Cu + -doped CdSe NCs, the Cu + impurity level has a predominately 3d character with a substantial 4p contribution.…”