Phonon-assisted upconversion photoluminescence of quantum emitters

Quantum emitters are widely used in quantum networks,quantum information processing,and quantum sensing due to their excellent optical properties.Compared with Stokes excitation,quantum emitters under anti-Stokes excitation exhibit better performance.In addition to laser cooling and nanoscale thermometry,anti-Stokes excitation can improve the coherence of single-photon sources for advanced quantum technologies.In this review,we follow the recent advances in phononassisted upconversion photoluminescence of quantum emitters and discuss the upconversion mechanisms,applications,and prospects for quantum emitters with anti-Stokes excitation.

Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition

The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration GaAs/A1GaAs semiconductor quantum dot are analytically studied with the phonon-assisted transition （PAT）. It is shown that the changes among a single electromagnetically induced transparency （EIT） window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT to. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications.

Phonon-assisted intersubband transitions in wurtzite GaN/In_x Ga_(1-x) N quantum wells

A detailed numerical calculation on the phonon-assisted intersubband transition rates of electrons in wurtzite CaN/InxGal-xN quantum wells is presented. The quantum-confined Stark effect, induced by the built-in electric field, and the ternary mixed crystal effect are considered. The electron states are obtained by iteratively solving the coupled SchrSdinger and Poisson equations. The dispersion properties of each type of phonon modes are considered in the derivation of Fermi＇s golden rule to evaluate the transition rates. It is indicated that the interface and half- space phonon scattering play an important role in the process of 1 2 radiative transition. The transition rate is also greatly reduced by the built-in electric field. This work can be helpful for the structural design and simulation of new semiconductor lasers.

General formula for phonon-assisted n-photon absorption in solids

A general formula for phonon-assisted n-photon absorption in solids is obtained by （n ＋ 1）-th order perturbation technique. The complicated calculation process for transition element of n-photon absorption is simply demonstrated by a diagram approach that is proposed in this work. We find that the transition element for the n-photon absorption has a simple form, i.e., it is just the first term of the n-th order fist kind Bessel function.

Phonon-Assisted Spin Current in Single Molecular Magnet Junctions

Owing to the bistable character of the single molecular magnet （SMM）, it can generate 100% spin-polarized currents even connected with normal （N） leads. In this work, we study the phonon-assisted spin current in N- SMM-N systems. We mainly focus on the interplay of SMM＇s bistable character and electron-phonon coupling. It is found that when SMM is trapped in one of the lowest bistable states, it can generate phonon-assisted spin- polarized currents. At the up-spin transport channel, it is accompanied by a phonon-assisted up-spin current, while at the down-spin transport channel, it is accompanied by a phonon-assisted down-spin current.

Impact of phonon-assisted tunneling on electronic conductivity in graphene nanoribbons and oxides ones

Phonon-assisted tunneling (PhAT) model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed model describes well not only current dependence on temperature but also the temperature-dependent I-V data using the same set of parameters characterizing material under investigation. The values of active phonons energy and field strength for tunneling are estimated from the fit of current dependence on temperature and I-V/T data with the phonon-assisted tunneling theory.

Color-tunable hypersensitive temperature sensor based on metal organic framework doped with Eu^(3+)and Dy^(3+)via phonon-assisted energy transfer

In this work,catena-[(μ-benzene-1,3,5-tricarboxylato)-(1,10-phenanthroline)-(N,N-dimethylfo rmamide)-gadolinium(ⅲ)-N,N-dimethylformamide solvate](denoted as Gd-MOF)co-doped with Eu^(3+)and Dy^(3+)was successfully synthesized.The entire X-ray diffraction peaks of the sample match well with the GdMOF phase.A detailed characterization by inductively coupled plasma mass spectrometry(ICP-MS)shows that the actual concentration is basically consistent with the design concentration.The temperature sensing properties of Gd-MOF:Eu^(3+),Dy^(3+)were analyzed by temperature-dependent fluorescence spectra from 213 to 453 K.As temperature rises,the emission color of Gd-MOF:Eu^(3+),Dy^(3+)changes from yellow to red.The relative sensitivity reaches a maximum of 5.87%/K at 383 K in the Gd-MOF:1%Eu^(3+),30%Dy^(3+)sample.The high relative sensitivity of this MOF is due to the phonon-assisted energy transfer from Dy^(3+)to Eu^(3+),which is proved via fluorescence decay curves and fluoresce nce spectra.The major route of this energy transfer is^(4)F_(9/2)(Dy^(3+))→^(5)D_(1)(Eu^(3+)).

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature： the self-absorption effect

It is firmly demonstrated in experiment that the self-absorption(SA) effect can lead to the extinction of the zero-phonon line and the first-order longitudinal optical phonon sideband of free excitonic luminescence of ZnO at room temperature. Moreover, effectiveness degree of SA effect is found to be dependent on both absorption coefficient and travelling distance of emitted photons, as well as even lattice temperature, which is uniquely reflected by the redshift amount in emission peak in ZnO. It is also unambiguously proved that the SA effect still strictly obeys the Beer-Lambert law of absorption. This work not only uncovers the long-term puzzle of significant redshift of emission peak of ZnO at higher temperatures, but also shows that the SA effect may have to be carefully taken into consideration in the study of spontaneous emission, laser and relevant optoelectronic processes in luminescent materials and optoelectronic devices.