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A series of lead-free Rb2ZrCl6:xTe4+ (x = 0%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 10.0%) perovskite materials were synthesized through a hydrothermal method in this work. The substitution of Te4+ for Zr in Rb2ZrCl6 was investigated to examine the effect of Te4+ doping on the spectral properties of Rb2ZrCl6 and its potential applications. The incorporation of Te4+ induced yellow emission of triplet self-trapped emission (STE). Different luminescence wavelengths were regulated by Te4+ concentration and excitation wavelength, and under a low concentration of Te4+ doping (x ≤ 0.1%), different types of host STE emission and Te4+ triplet state emission could be achieved through various excitation energies. These luminescent properties made it suitable for applications in information encryption. When Te4+ was doped at high concentrations (x ≥ 1%), yellow triplet state emission of Te4+ predominated, resulting in intense yellow emission, which stemmed from strong exciton binding energy and intense electron-phonon coupling. In addition, a Rb2ZrCl6:2%Te4+@RTV scintillating film was fabricated and a spatial resolution of 3.7 lp/mm was achieved, demonstrating the potential applications of Rb2ZrCl6:xTe4+ in nondestructive detection and bioimaging. [ABSTRACT FROM AUTHOR]

The 2D semiconductors are an ideal platform for exploration of bosonic fluids composed of coupled photons and collective excitations of atoms or excitons, primarily due to large excitonic binding energies and strong light‐matter interaction. Based on first‐principles calculations, it is demonstrated that the phonon polaritons formed by two infrared‐active phonon modes in monolayer MoSi2N4 and WSi2N4 possess ultra‐high confinement factors of around ≈105 and 103, surpassing those of conventional polaritonic thin‐film materials by two orders of magnitude. It is observed that the first bright exciton possesses a substantial binding energies of 750 and 740 meV in these two monolayers, with the radiative recombination lifetimes as long as 25 and 188 ns, and the Rabi splitting of the formed cavity‐exciton polaritons reaching 373 and 321 meV, respectively. The effective masses of the cavity exciton polaritons are approximately 10−5me, providing the potential for high‐temperature quantum condensation. The ultra‐confined and ultra‐low‐loss phonon polaritons, as well as strongly‐coupled cavity exciton polaritons with ultra‐small polaritonic effective masses in these two monolayers, offering the flexible control of light at the nanoscale, probably leading to practical applications in nanophotonics, meta‐optics, and quantum materials. [ABSTRACT FROM AUTHOR]

The first-order phase transition between the liquid and gaseous phases ends at a critical point. Critical opalescence occurs at this singularity. Discovered in 1822, it is known to be driven by diverging fluctuations in the density. During the past two decades, boundaries between the gas-like and liquid-like regimes have been theoretically proposed and experimentally explored. Here, we show that fast cooling of near-critical sulfur hexafluoride (SF6), in presence of Earth's gravity, favors dark opalescence, where visible photons are not merely scattered, but also absorbed. When the isochore fluid is quenched across the critical point, its optical transmittance drops by more than three orders of magnitude in the whole visible range, a feature which does not occur during slow cooling. We show that transmittance shows a dip at 2eV near the critical point, and the system can host excitons with binding energies ranging from 0.5 to 4 eV. The spinodal decomposition of the liquid-gas mixture, by inducing a periodical modulation of the fluid density, can provide a scenario to explain the emergence of this platform for coupling between light and matter. The possible formation of excitons and polaritons points to the irruption of quantum effects in a quintessentially classical context. The first-order phase boundary between the liquid and gaseous phases ends at a critical point where the fluid, kept at thermodynamic equilibrium, displays a turbidity known as 'critical opalescence'. The authors quench a fluid across its critical point, find blackness instead of turbidity, and argue that, out of equilibrium, photons can be absorbed, not merely scattered. [ABSTRACT FROM AUTHOR]

Due to its tunable bandgap, anisotropic behavior, and superior thermoelectric properties, device applications using layered tellurene (Te) are becoming more attractive. Here, we report a thinning technique for exfoliated tellurene nanosheets using thermal annealing in an oxygen environment. We characterize different thinning parameters, including temperature and annealing time. Based on our measurements, we show that controlled layer thinning occurs in the narrow temperature range of 325–350 °C. We also show a reliable method to form β-tellurene oxide (β-TeO2), which is an emerging wide bandgap semiconductor with promising electronic and optoelectronic properties. This wide bandgap semiconductor exhibits a broad photoluminescence (PL) spectrum with multiple peaks covering the range of 1.76–2.08 eV. This PL emission, coupled with Raman spectra, is strong evidence of the formation of 2D β-TeO2. We discuss the results obtained and the mechanisms of Te thinning and β-TeO2 formation at different temperature regimes. We also discuss the optical bandgap of β-TeO2 and show the existence of pronounced excitonic effects evident by the large exciton binding energy in this 2D β-TeO2 system that reach 1.54–1.62 eV for bulk and monolayer, respectively. Our work can be utilized to have better control over the Te nanosheet thickness. It also sheds light on the formation of well-controlled β-TeO2 layered semiconductors for electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Carbon nitrides form a series of polymer semiconductors popular in photocatalysis. In the course of photoresponse, the separation of light-induced electron–hole pairs is one of the critical factors that affect the conversion rate from photoenergy to chemical substance. Exciton binding energy ( E b ) is treated as a classical parameter to evaluate the barrier of exciton dissociation. In this work, we study the electronic and optical nature of two specific members of the carbon nitride family, polymeric carbon nitride (melon) and crystallized poly(triazine imide) (PTI/Li+Cl−) by employing the photoluminescence spectra and density functional theory (DFT) calculations based on the Wannier-Mott exciton module. The results of self-consistent GW computation were applied. The measurement of photoluminescence spectra, by which exciton binding energies are estimated, is likewise discussed. Generally, compared with the results calculated by GW-BSE, the DFT results based on the Wannier-Mott model are closer to the experimental values. From a materials perspective, on the other hand, the exciton binding energy of the melon is lower than that of PTI/Li+Cl−. [ABSTRACT FROM AUTHOR]

A library of large organic cation spacers is available for engineering the performance of layered two‐dimensional (2D) halide perovskite devices. Despite extensive photophysics studies, there remains a research gap over the structure‐function relations in 2D perovskites, especially the underlying factors influencing the Auger recombination (AR) process. Herein, the contributions of exciton binding energy, exciton‐phonon coupling, and defects/film morphology to the AR process in 2D perovskites are examined. Phenyl‐alkyl‐ammonium cations with different lengths of attached alkyl groups, commonly used in blue light‐emitting diodes, are investigated. The findings reveal an order of magnitude higher threshold carrier density for the AR onset as well as a reduced AR in cations with longer alkyl chain length. Although possessing similar exciton binding energies, the exciton‐phonon coupling strength is found to play a major role in reducing the AR rate, with a smaller contribution from the defect states/film morphology. The findings can help provide further guidance on organic spacer cation engineering for highly efficient 2D perovskite light emitters. [ABSTRACT FROM AUTHOR]

An evolutionary algorithm was employed to locate the global minimum of Ti O 2 n nanoparticles with n = 2 – 20. More than 61,000 structures were calculated with a semiempirical method and reoptimized using density functional theory. The exciton binding energy of TiO2 nanoparticles was determined through the fundamental and optical band gap. Frenkel exciton energy scales as E B eV = 8.07 / n 0.85 , resulting in strongly bound excitons of 0.132–1.2 eV for about 1.4 nm nanoparticles. Although the exciton energy decreases with the system size, these tightly bound Frenkel excitons inhibit the separation of photogenerated charge carriers, making their application in photocatalysis and photovoltaic devices difficult, and imposing a minimum particle size. In contrast, the exciton binding energy of rutile is 4 meV, where the Wannier exciton energy scales as E B eV = 13.61 μ / ε 2 . Moreover, the Wannier excitons in bulk TiO2 are delocalized according to the Bohr radii: 3.9 nm for anatase and 7.7 nm for rutile. [ABSTRACT FROM AUTHOR]

Adsorption‐photocatalysis technology based on covalent organic frameworks (COFs) offers an alternative method for advancing the field of uranium extraction from seawater. When determining the photocatalytic activity of COFs, the binding energy of excitons (Eb) functions is the decisive factor. Nevertheless, the majority of reported COFs have a large Eb, which seriously restricts their application in the field of photocatalysis. Using a practical π‐skeleton engineering strategy, the current study synthesizes three donor‐acceptor olefin‐linked COFs containing amidoxime units in an effort to minimize Eb. Theoretical and experimental results reveal that the construction of planar and continuous π‐electron delocalization channels can significantly reduce Eb and promote the separation of electron‐hole pairs, thereby enhancing the photocatalytic activities. Moreover, the Eb of the TTh‐COF‐AO with a planar π‐skeleton donor is significantly reduced, and exhibits a substantially smaller Eb (38.4 meV). Under visible light irradiation, a high photo‐enhanced uranium extraction capacity of 10.24 mg g−1 is achieved from natural seawater without the addition of sacrificial reagents, which is superior to the majority of olefin‐linked COFs that have been reported to date. This study, therefore, paves the way for the development of tailored, efficient COFs photocatalysts for the extraction of uranium from seawater. [ABSTRACT FROM AUTHOR]

• Single-atom Co loaded on silver birch leaf-like COF framework (COF-Co X) was obtained. • The formation of Co-N sites boost exciton dissociation and charge transfer. • COF-Co10 shows impressive peroxymonosulfate activation to degrade tetracycline. Covalent organic framework (COF) materials have received extensive attention in the field of photocatalysis in recent years, but the strong exciton effect in COF has seriously affected the separation of electron-hole pairs so that limiting the enhancement of the photocatalytic performance. It is of great significance to explore suitable ways to regulate the exciton behavior in COF materials and enhance their electron-hole's separation efficiency. By anchoring Co single-atoms within a silver birch leaf-like COF framework (COF-Cox), the exciton in COF is effectively dissociated by forming Co-N sites, producing massive free electrons and holes. Co-N sites also facilitate photogenerated holes aggregation toward Co single-atoms, which effectively drives the carriers' separation in COF framework. The carrier concentration of COF-Co10 is 2.81 times higher compared with the original COF. The reduced exciton binding energy (E b) further proves that the the formation of Co-N sites promote the exciton dissociation. Consequently, COF-Cox can well activate peroxymonosulfate (PMS) to degrade tetracycline (TC) pollutants, the reaction rate constant of COF-Co10 (3.65 × 10-2 min−1) is 5.27 times higher than COF (6.93 × 10-3 min−1). The possible activation routes and degradation products of TC are also discussed. This study provides a more comprehensive understanding of the exciton behavior for the design of more efficient COF-based catalysts. [ABSTRACT FROM AUTHOR]

The ground state, the fundamental transition, and the binding energies of heavy hole and light hole excitons confined in GaNAsBi/GaAs strained spherical quantum dots (QDs) are calculated. Computing is based on the variational method within the effective mass approximation, combined with the band anti-crossing model. Moreover, the exciton effective Bohr radius a B * is determined using two methods: (i) the radial probability density and (ii) the reciprocal variational parameter, and the limits of these methods are discussed. Theoretical computations of exciton diamagnetic coefficients σ are also presented and compared to the literature. Both excitons optoelectronic and diamagnetic parameters dependence on QD radii R in the range 2–14 nm, and nitrogen and bismuth contents (up to 12%) is obtained with respect to confinement conditions of electric charge carriers, tensile and compressive strain effects, and Coulomb's interaction. We find that the increase of a B * (R) is nearly linear and a B * < R for the pair (x N , y B i ) = (4 , 5) % , but a B * can exceed R for high concentrations of N and Bi. Besides, for a typical sphere radius of 4 nm, GaN x As 1-x-y Bi y /GaAs QDs exhibit broadband emission in the infrared wavelength range of about 1.03–2.55 μm which covers particularly the telecommunication wavelengths of 1.3 and 1.55 μm. By adjusting the adequate dot size and alloy contents, the operating spectral domain can be enlarged, and the emission wavelength can be controlled for several infrared applications. [ABSTRACT FROM AUTHOR]