The radiance of thermal emission, as described by Plancks law, depends only on the emissivity and temperature of a body, and increases monotonically with temperature rise at any emitted wavelength. Nonthermal radiation, such as photoluminescence (PL), is a fundamental light matter interaction that conventionally involves the absorption of an energetic photon, thermalization, and the emission of a redshifted photon. Until recently, the role of rate conservation when thermal excitation is significant, has not been studied in any nonthermal radiation. A question: What is the overall emission rate if a high quantum efficiency (QE), PL material, is heated to a temperature where it thermally emits a rate of 50 photons/sec at its bend edge, while in parallel is PL excited at a rate of 100 photons/sec. Recently, we discovered that the answer is an overall rate of 100 blueshifted photons/sec. In contrast to thermal emission, the PL rate is conserved with temperature increase, while each photon is blueshifted. Further rise in temperature leads to an abrupt transition to thermal emission where the photon rate increases sharply. These findings show that PL is an ideal optical heat pump. Here we study, for the first time, the emission rate of PL radiation at moderate QE where nonradiative processes dominate the dynamics. Though conservation of photon rate does not apply, we predict that the emission rate at 100% QE is an upper limit for the overall emission rate regardless of the QE. Also, the transition temperature to thermal emission is QE independent.
Probing temperature dependent non-radiative decay channels in CrSBr with nonlinear optics
Southwest University of Science and Technology（西南科技大学）；Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学）；University of Electronic Science and Technology of China（电子科技大学）；University of Münster（明斯特大学）；University of Chemistry and Technology Prague（布拉格化工大学）；Argonne National Laboratory（阿贡国家实验室）；University of Chicago（芝加哥大学）；Massachusetts Institute of Technology（麻省理工学院）；Abbe Center of Photonics, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学阿贝光子学中心）
The approach based on the generalized Kirchhoff's law for calculating photoluminescence (PL) spectra of one-dimensional (1D) multi-layered structures, in particular, 1D photonic crystals has been developed. It is valid in the local thermodynamic equilibrium approximation and leads to simple and explicit expression for the photoluminescence intensity. In the framework of the present theory the analytical expression for the spontaneous emission intensity enhancement factor (IEF) for a 1D photonic crystal has been derived. It takes a particularly simple form in the case of a sufficiently large nu…
In atomically thin semiconductors, localized exciton (X$_L$) coupled to light shows single quantum emitting behaviors through radiative relaxation processes providing a new class of optical sources for potential applications in quantum communication. In most studies, however, X$_L$ photoluminescence (PL) from crystal defects has mainly been observed in cryogenic conditions because of their sub-wavelength emission region and low quantum yield at room temperature. Furthermore, engineering the radiative relaxation properties, e.g., emission region, intensity, and energy, remained challenging. Her…
In this work we develop a simple theory for the green photoluminescence of ZnO quantum dots (QDs) that allows us to understand and rationalize several experimental findings on fundamental grounds. We calculate the spectrum of light emitted in the radiative recombination of a conduction band electron with a deeply trapped hole and find that the experimental behavior of this emission band with particle size can be understood in terms of quantum size effects of the electronic states and their overlap with the deep hole.We focus the comparison of our results on detailed experiments performed for c…
Swiss Federal Institute of Technology Lausanne (EPFL)（洛桑联邦理工学院）；Shanghai Jiao Tong University (SJTU)（上海交通大学）；The Hong Kong University of Science and Technology（香港科技大学）
Continuous and concerted development of colloidal quantum-dot light-emitting diodes over the past two decades has established them as a bedrock technology for the next generation of displays. However, a fundamental issue that limits the performance of these devices is the quenching of photoluminescence due to excess charges from conductive charge transport layers. Although device designs have leveraged various workarounds, doing so often comes at the cost of limiting efficient charge injection. Here we demonstrate that high-field terahertz (THz) pulses can dramatically brighten quenched QDs on…
Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by a very large oscillator strength. Encapsulation of monolayers such as MoSe$_2$ in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. We demonstrate that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. The time-resolved photoluminescence measurements together with cw reflectivity and …
Thermal quenching is one of the essential factors in reducing the efficiency of radiative processes in luminophores of various nature. The emission activity of low dimensional structures is influenced also by multiplicity of parameters that are related to synthesis processes, treatment regimes, etc. In the present work, we have investigated the temperature dependence of photoluminescence caused by exciton and defect-related transitions in ensembles of biocompatible InP/ZnS core/shell nanocrystals with an average size of 2.1 and 2.3 nm. The spread in the positions of energy levels is shown to b…
Er-doped aluminum nitride films, containing different Er concentrations, were obtained at room temperature by reactive radio frequency magnetron sputtering. The prepared samples show a nano-columnar microstructure and the size of the columns is dependent on the magnetron power. The Er-related photoluminescence (PL) was studied in relation with the temperature, the Er content and the microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved PL were performed. Both visible and near infrared PL were obtained at room temperature for the as-deposited samples. It is demonstrated …
Compared to traditional nonlinear optical crystals, like BaB$_2$O$_4$, KTiOPO$_4$ or LiNbO$_3$, semiconductor integrated sources of photon pairs may operate at pump wavelengths much closer to the bandgap of the materials. This is also the case for Bragg-reflection waveguides (BRW) targeting parametric down-conversion (PDC) to the telecom C-band. The large nonlinear coefficient of the AlGaAs alloy and the strong confinement of the light enable extremely bright integrated photon pair sources. However, under certain circumstances, a significant amount of detrimental broadband photoluminescence ha…
The interaction between light and metal nanoparticles enables investigations of microscopic phenomena on nanometer length and ultrashort time scales, benefiting from strong confinement and enhancement of the optical field. However, the ultrafast dynamics of these nanoparticles are primarily investigated by multiphoton photoluminescence on picoseconds or photoemission on femtoseconds independently. Here, we presented two-photon photoluminescence (TPPL) measurements on individual Au nanobipyramids (AuNP) to reveal their ultrafast dynamics by two-pulse excitation on a global time scale ranging fr…
Turning on the Light: Polymorphism-Induced Photoluminescence in Cysteine Crystals
International Centre for Theoretical Physics (ICTP)（国际理论物理中心）；The George S. Wise Faculty of Life Sciences, Tel Aviv University（特拉维夫大学乔治·S·怀斯生命科学学院）；The Hebrew University of Jerusalem（耶路撒冷希伯来大学）；Bar-Ilan University（巴伊兰大学）；Weizmann Institute of Science（魏茨曼科学研究所）
