Pushing the Band Gap Envelope of Quasi-Type II Heterostructured Nanocrystals to Blue: ZnSe/ZnSe _{1- X} Te _X /ZnSe Spherical Quantum Wells

Abstract

Quasi-type II heterostructured nanocrystals (NCs) have been of particular interest due to their great potential for controlling the interplay of charge carriers. However, the lack of material choices for quasi-type II NCs restricts the accessible emission wavelength from red to near-infrared (NIR), which hinders their use in light-emitting applications that demand a wide range of visible colors. Herein, we demonstrate a new class of quasi-type II nanoemitters formulated in ZnSe/ZnSe1-XTeX/ZnSe seed/spherical quantum well/shell heterostructures (SQWs) whose emission wavelength ranges from blue to orange. In a given geometry, ZnSe1-XTeX emissive layers grown between the ZnSe seed and the shell layer are strained to fit into the surrounding media, and thus, the lattice mismatch between ZnSe1-XTeX and ZnSe is effectively alleviated. In addition, composition of the ZnSe1-XTeX emissive layer and the dimension of the ZnSe shell layer are engineered to tailor the distribution and energy of electron and hole wave functions. Benefitting from the capabilities to tune the charge carriers on demand and to form defect-free heterojunctions, ZnSe/ZnSe1-XTeX/ZnSe/ZnS NCs show near-unity photoluminescence quantum yield (PL QY>90%) in a broad range of emission wavelengths (peak PL from 450 nm to 600 nm). Finally, we exemplify dichromatic white NC-based light-emitting diodes (NC-LEDs) employing the mixed layer of blue- and yellow-emitting ZnSe/ZnSe1-XTeX/ZnSe/ZnS SQW NCs.

Impact of Morphological Inhomogeneity on Excitonic States in Highly Mismatched Alloy ZnSe1–XTeX Nanocrystals

“…Interestingly, we find that the spectral shift results from an emergence of additional peaks at lower-energy positions, approximately >110 meV apart from the apex, rather than the gradual shift of the main peak, which is evident in asymmetric PL spectral profiles for NCs with non-zero Te content. In fact, the additional peaks on the lower-energy side of PL spectra have been commonly observed in ZnSe 1– X Te X -based NCs whose PL peak emission lies in the blue region [450–470 nm (2.64–2.76 eV)]. − This phenomenon is responsible for the sudden broadening of the spectral line width (fwhm) from 110 meV (16 nm) for X = 0 to 260 meV (44 nm) for X = 0.08.…”

Recent Progress in Halide Perovskite Radiation Detectors for Gamma-Ray Spectroscopy

“…Commonly used materials for scintillators include inorganic scintillators (CsI, NaI:Tl, and many others) and organic scintillators (organic crystals, liquid, and plastic scintillators). Recently, perovskite single crystals (SCs) and nanocrystals (NCs) have been found to be promising materials for scintillation, especially for X-ray imaging purpose. , Following the surge of interest in lead halide perovskites in the various fields, the corresponding colloidal NCs have been intensively developed. − These NCs have high photoluminescence quantum yields, even when no specific surface treatments are performed on them. This peculiar feature arises from their unique electronic structure, such that surface trap states, mainly arising from halide ion vacancies, either are nested in the valence/conduction band or form shallow levels.…”

Deciphering Ultrafast Carrier Dynamics of Eco-Friendly ZnSeTe-Based Quantum Dots: Toward High-Quality Blue–Green Emitters

“…With relatively less difference in the electron mass m e * of ZnSe and ZnTe and little amount of Te doping on ZnSe to form the ZnSeTe core, the conduction band offsets at the interface of ZnSeTe/ZnSe are similar to the thermal energy of room temperature, allowing the electrons to leak from the core, while the valence band is dramatically elevated, which accretes a prominent energetic barrier for holes to delocalize, principally deriving from the large difference in effective mass of heavy hole m hh * between ZnSe and ZnTe. A recent theoretical work pointed out this asymmetric change in conduction and valence band-edge energy level of ZnSeTe along with Te contents, which may result in quasi-type II band alignment across the ZnSe and ZnSeTe layer. In the case of the thick-shell CQDs, the inner ZnSe and intermediate ZnSeS shell may serve as buffer layers to minimize the energy level difference between the ZnSeTe core and the outermost protective shell ZnS, to further shift the conduction band as a structural template for quasi-type II CQDs.…”

“…While for the thick-shell sample with high PLQY, the fast decay process is largely suppressed, which indicates that the fast component of 6.1 ps corresponds to the carrier trapping process and the slow component relates to the long-lived radiative exciton recombination. Because the effective mass of the electron is much smaller than that of the hole in II–VI CQDs, , the PB signal is expected to originate mainly from the state-filling effect of electrons. Therefore, the suppression of the fast decay (6.1 ps) process indicates the effective passivation of band-edge electron traps in the thick-shell sample.…”