arXiv subjects

Bolong Huang

Publications and source records attributed to Bolong Huang.

5 recordsLinked to original sources

arXiv2024

Broadband NIR photon upconversion generates NIR persistent luminescence for bioimaging

Upconversion persistent luminescence (UCPL) phosphors that can be directly charged by near-infrared (NIR) light have gained considerable attention due to their promising applications ranging from photonics to biomedicine. However, current lanthanide-based UCPL phosphors show small absorption cross-sections and low upconversion charging efficiency. The development of UCPL phosphors faces challenges of lacking flexible upconversion charging pathways and poor design flexibility. Herein, we discovered a new lattice defect-mediated broadband photon upconversion process and the accompanied NIR-to-NIR UCPL in Cr-doped zinc gallate nanoparticles. The zinc gallate nanoparticles can be directly activated by broadband NIR light in the 700-1000 nm range to produce persistent luminescence at about 700 nm, which is also readily enhanced by rationally tailoring the lattice defects in the phosphors. This proposed UCPL phosphors achieved a signal-to-background ratio of over 200 in bioimaging by efficiently avoiding interference from autofluorescence and light scattering. Our findings reported the lattice defect-mediated photon upconversion for the first time, which significantly expanded the horizons for the flexible design of NIR-to-NIR UCPL phosphors toward broad applications.

physics.optics↗

arXiv2015

Modeling the self-energy and wavefunction relaxation in the orbitals

The strong boundary normalized condition of wavefunction for fully occupied semicore 3d orbitals leads the linear response DFT+U on such metal oxide to have an insurmountable obstacle in Hubbard U determination. We treated the orbital self-energy and orbital relaxation as components of eigenvalues with respective orbital occupation number that follows the Fermi-Dirac distribution. By self-consistently solving the second partial deviation of total energy based on the most simple local density formalism with Hubbard U correction, we found the local density exchange-correlation potential functional can only give a minimized residue of the self-energy and orbital relaxation on the focus orbital if the Janak theorem maintained. Such residue turns to well counteracted in the fully occupied orbitals and non-zero the partially occupied orbitals. With keeping the validation of Janak theorem on localized orbitals, the self-consistent cycle by local density functional with Hubbard U correction cannot find out a set of orbital occupation that simultaneously offsets the orbital self-energy and relaxations in the empty and partially filled shell, but returns a unique set of the occupation for fully occupied shell. The band gap calculations on fully occupied orbital based compounds are thus improved and the relaxed lattices are also shown based on minimization of the self-energy error, which shows a possible route for accurate excited state studies.

cond-mat.str-el↗

arXiv2015

4f fine-structure levels as the dominant error in the electronic structures of binary lanthanide oxides

The ground-state 4f fine-structure levels in the intrinsic optical transition gaps between the 2p and 5d orbitals of lanthanide sesquioxides (Ln2O3, Ln=La...Lu) were calculated by a two-way crossover search for the U parameters for DFT+U calculations. The original 4f-shell potential perturbation in the linear response method were reformulated within the constraint volume of thegiven solids. The band structures were also calculated. This method yields nearly constant optical transition gaps between Ln-5d and O-2p orbitals, with magnitudes of 5.3~5.5 eV. This result verifies that the error in the band structure calculations for Ln2O3 is dominated by the inaccuracies in the predicted 4f levels in the 2p-5d transition gaps, which strongly and nonlinearly depend on the on-site Hubbard U. The relationship between the 4f occupancies and Hubbard U is non-monotonic and is entirely different from that for materials with 3d or 4d orbitals, such as transition metal oxides. This new linear response DFT+U method can provide a simpler understanding of the electronic structure of Ln2O3 and enables a quick examination of the electronic structures of lanthanide solids prior to hybrid functional or GW calculations.

cond-mat.str-el↗

arXiv2015

Intrinsic deep hole trap levels in $Cu_{2}O$ with self-consistent repulsive Coulomb energy

The large error of the DFT+U method on full-filled shell metal oxides is due to the residue of self-energy from the localized d orbitals of cations and p orbitals of the anions. U parameters are self-consistently found to achieve the analytical self-energy cancellation. The improved band structures based on relaxed lattices of ${Cu_{2}O}$ are shown based on minimization of self-energy error. The experimentally reported intrinsic p-type trap levels are contributed by both Cu-vacancy and the O-interstitial defects in ${{Cu}_{2}O}$. The latter defect has the lowest formation energy but contributes a deep hole trap level while the Cu-vacancy has higher energy cost but acting as a shallow acceptor. Both present single-particle levels spread over nearby the valence band edge, consistent to the trend of defects transition levels. By this calculation approach, we also elucidated the entanglement of strong p-d orbital coupling to unravel the screened Coulomb potential of fully filled shells.

cond-mat.mtrl-sci↗

arXiv2015

Native point defects in CaS: A focus on doping limit for persistent luminescence

We studied native point defects in CaS by DFT+ Hubbard U method. The effect of the localization of the d orbitals of Ca pseudopotential has been included. The Hubbard U corrected d-orbital for Ca sites are playing a role assisting the charge transfer from p orbitals of S site to the Ca site, giving both localized electron and hole states within the band gap, with an energy interval of 1.2~1.4 eV. This corresponds to the localized excitonic levels below the conduction band edge for the optical absorption. The electronic properties and formation energies of native point defects have been discussed. We found the neutral S vacancy has the lowest energy of 0.62 eV under Ca-rich limit. The Schottky defect pair defect is another dominant defect with cost of 1.51 eV per defect site from S-rich to Ca-rich chemical potential limits. The defect formation energy further summarized that the doubly positive S vacancy and doubly negative Ca vacancy are both the most stable donor-type and acceptor-type defects respectively coexisting in CaS. We also summarized a narrow doping limit energy which has been determined as 1.33 eV constantly in CaS independent to different chemical potential limits. But such doping allowed range entirely shifts from valence band vicinity toward the conduction band edge from S-rich to Ca-rich limits. Under S-rich limit, the dopable range for EF shifting corresponds to Eu2+ doping experiments, the luminescence wavelength limit is predicted to be 659 nm (1.88 eV) remarkably close to the reported results 650 nm. This gives a solid theoretical reference for the lanthanide ions doping experiments in CaS. We conclude that the defect levels combined with formation energy is an accessible way to suggest the doping energy range and an assistant to explain the activation stage of photostimulated luminescence (PSL) mechanism in lanthanide ions doped crystal materials.

cond-mat.mtrl-sci↗