arXiv subjects

Zhifeng Shi

Publications and source records attributed to Zhifeng Shi.

6 recordsLinked to original sources

arXiv2025

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability and adjustable optical properties. NIR emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, we summarize several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, and assess their recent advancements. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. We also highlight the various applications of NIR-emitting metal halides and provide an outlook for the field.

cond-mat.mtrl-sci↗

arXiv2025

Light-Emitting Diodes based on Metal Halide Perovskite and Perovskite Related Nanocrystals

Light-emitting diodes (LEDs) based on halide perovskite nanocrystals have attracted extensive attention due to their considerable luminescence efficiency, wide color gamut, high color purity, and facile material synthesis. Since the first demonstration of LEDs based on MAPbBr3 nanocrystals were reported in 2014, the community has witnessed a rapid development in their performances. In this review, we provide a historical perspective of the development of LEDs based on halide perovskite nanocrystals and then present a comprehensive survey of current strategies to high-efficiency lead-based perovskite nanocrystals LEDs, including synthesis optimization, ion doping/alloying and shell coating. We then review the basic characteristics and emission mechanisms of lead-free perovskite and perovskite-related nanocrystals emitters in environmentally friendly LEDs, from the standpoint of different emission colors. Finally, we cover the progress in LED applications and provide an outlook of the opportunities and challenges for future developments in this field.

cond-mat.mtrl-sci↗

arXiv2020

Quarkonium at non-zero isospin density

We calculate the energies of quarkonium bound states in the presence of a medium of nonzero isospin density using lattice QCD. The medium, created using a canonical (fixed isospin charge) approach, induces a reduction of the quarkonium energies. As the isospin density increases, the energy shifts first increase and then saturate. The saturation occurs at an isospin density close to that where previously a qualitative change in the behaviour of the energy density of the medium has been observed, which was conjectured to correspond to a transition from a pion gas to a Bose-Einstein condensed phase. The reduction of the quarkonium energies becomes more pronounced as the heavy-quark mass is decreased, similar to the behaviour seen in two-colour QCD at non-zero quark chemical potential. In the process of our analysis, the $η_b$-$π$ and $Υ$-$π$ scattering phase shifts are determined at low momentum. An interpolation of the scattering lengths to the physical pion mass gives $a_{η_b,π} = 0.0025(8)(6)$ fm and $a_{Υ,π} = 0.0030(9)(7)$ fm.

hep-lat↗

arXiv2012

LQCD at non zero isospin chemical potential

Systems of non-zero isospin chemical potential are studied from a canonical approach by computing correlation functions with the quantum numbers of $N π^+$'s ($C_{N π}$). In order to reduce the number of contractions required in calculating $C_{N π}$ for a large $N$ in the Wick's theorem, we constructed a few new algorithms. With these new algorithms, systems with isospin charge up to 72 are investigated on three anisotropic gauge ensembles with a pion mass of $390 \rm{MeV}$, and with lattice spatial extents $L \sim {2.0, 2.5, 3.0} \rm{fm}$. The largest isospin density of $ρ_I \approx 9 \rm{fm}^{-3}$ is achieved in the smallest volume, and the QCD phase diagram is investigated at a fixed low temperature at varying isospin chemical potentials, $m_π \le μ_I \le 4.5 m_π$. By investigating the behaviour of the extracted energy density of the system at different isospin chemical potentials, we numerically identified the conjectured transition to a Bose-Einstein condensation state at $μ_I \ge m_π$.

hep-lat↗

arXiv2012

Lattice QCD at non-zero isospin chemical potential

Quantum chromodynamics (QCD) at non-zero isospin chemical potential is studied in a canonical approach by analyzing systems of fixed isospin number density. To construct these systems, we develop a range of new algorithms for performing the factorially large numbers of Wick contractions required in multi-hadron systems. We then use these methods to study systems with the quantum numbers of up to 72 $π^+$'s on three ensembles of gauge configurations with spatial extents $L\sim$ 2.0, 2.5 and 3.0 fm, and light quark masses corresponding to a pion mass of {390 MeV}. The ground state energies of these systems are extracted and the volume dependence of these energies is utilized to determine the two- and three- body interactions amongst $π^+$'s. The systems studied correspond to isospin densities of up to $ρ_I\sim 9\ {\rm fm}^{-3}$ and probe isospin chemical potentials, $μ_I$, in the range $m_π \lsim μ_I\ \lsim 4.5\ m_π$, allowing us to investigate aspects of the QCD phase diagram at low temperature and for varying isospin chemical potential. By studying the energy density of the system, we provide numerical evidence for the conjectured transition of the system to a Bose-Einstein condensed phase at $μ_I\ \gsim m_π$.

hep-lat↗

arXiv2011

Investigations of QCD at non-zero isospin density

We investigate the QCD phase diagram as a function of isospin chemical potential at a fixed temperature by directly putting large numbers of π^+s into the system. Correlation functions of N π^+s systems involves N!N! contractions, and become extremely expensive when N is large. In order to alleviate this problem, a recursion relation of correlation functions has been derived in Ref. [1] that substantially reduces the number of independent contractions needed and makes the study of many pions systems be possible. In this proceeding this method is investigated numerically. We have also constructed a new method that is even more efficient, enabling us to study systems of up to 72 π^+s.

hep-lat↗