Impact of excitation energy on the excitonic luminescence of cesium lead bromide perovskite nanosheets.

An excitation-energy-dependent luminescence phenomenon is reported in cesium lead bromide (CsPbBr3) perovskite nanosheets. At 10 K, the relative integrated luminescence intensity between the trapped exciton (TX) emission and the free exciton (FX) emission shows an interesting tendency with increasing the optical excitation energy from 2.431 eV (510 nm) to 3.758 eV (330 nm). To interpret such phenomenon, we develop a quantitative model on the basis of the biological population growth theory. A good agreement between experiment and theory is obtained. It is thus revealed that the lower capture coefficient of the TX level to the excited excitons via multiphonon emission relative to the FX level shall be the major cause of the observed phenomenon. These findings may help to deepen the current understanding of the complex luminescence mechanisms of these emerging light-emitting materials.

Photoluminescence signatures of thermal expansion, electron-phonon coupling and phase transitions in cesium lead bromide perovskite nanosheets.

In this article, photoluminescence (PL) behaviors of inorganic cesium lead bromide (CsPbBr3) nanosheets are investigated in a broad temperature range from 5 to 500 K. As can be seen from the temperature evolution of the PL peak position, the bandgap blueshift induced by thermal lattice expansion is found to be gradually compensated by the bandgap redshift caused by electron-phonon coupling for the temperature variation from 5 K to 360 K. As the temperature is further increased, the nearly completely compensated PL peak position turns to exhibit a rapid blueshift, again at ∼360 K. Such turning behavior is consistent with an orthorhombic-tetragonal (γ-ß) phase transition at this critical temperature. For the PL linewidth, it shows a continuous broadening at temperatures beyond 40 K, suggesting the dominant role of phonon scattering, especially at high temperatures. These findings of temperature dependent photophysical properties of CsPbBr3 nanosheets may provide useful information of their further applications in the emerging nano photo-electronic devices.

Dopant-Induced Electric Fields and Their Influence on the Band-Edge Absorption of GaN.

Dopant-induced local electric fields and their influence on the band-edge absorption of GaN are theoretically examined. For dopant-induced electric field distribution, it is derived with Bayes' rule. For the average electric field strength, it is revealed to be quite strong, i.e., in an order of 104 V/cm in GaN with a fairly low dopant density. On the basis of the Franz-Keldysh mechanism, influence of the dopant-induced electric fields on the band-edge absorption coefficient of GaN is then investigated. Without any adjustable parameters, absorption coefficients of GaN are computed and in good agreement with the available experimental values.

Luminescence Anisotropy and Thermal Effect of Magnetic and Electric Dipole Transitions of Cr3+ Ions in Yb:YAG Transparent Ceramic.

In this article, we present an in-depth optical study on luminescence spectral features and the thermal effect of the magnetic dipole (MD) transitions (e.g., the R lines of 2E → 4A2) and the associated electric dipole transitions (e.g., phonon-induced sidebands of the R lines) of Cr3+ ions in ytterbium-yttrium aluminum garnet polycrystalline transparent ceramic. The doubly split R lines predominately due to the doublet splitting of the 2E level of the Cr3+ ion in an octahedral crystal field are found to show a very large anisotropy in both emission intensity and thermal broadening. The large departure from the intensity equality between them could be interpreted in terms of large difference in coupling strength with phonons for the doubly split states of the 2E level. For the large anisotropy in thermal broadening, very different effective Debye temperatures for the two split states may be responsible for it. Besides the 2E excited state, the higher excited states, for example, 4T1 and 4T2 of the Cr3+ ion, also exhibit a very large inequality in coupling strength with phonons at room temperature. By examining the Stokes phonon sidebands of the MD R lines at low temperatures with the existing ion-phonon coupling theory, we reveal that they indeed carry fundamental information of phonons. For example, their broad background primarily reflects Debye density of states of acoustic phonons. These new results significantly enrich our existing understanding on interesting but challenging luminescence mechanisms of ion-phonon coupling systems.

Hierarchical assembly of centriole subdistal appendages via centrosome binding proteins CCDC120 and CCDC68.

In animal cells, the centrosome is the main microtubule-organizing centre where microtubules are nucleated and anchored. The centriole subdistal appendages (SDAs) are the key structures that anchor microtubules in interphase cells, but the composition and assembly mechanisms of SDAs are not well understood. Here, we reveal that centrosome-binding proteins, coiled-coil domain containing (CCDC) 120 and CCDC68 are two novel SDA components required for hierarchical SDA assembly in human cells. CCDC120 is anchored to SDAs by ODF2 and recruits CEP170 and Ninein to the centrosome through different coiled-coil domains at its N terminus. CCDC68 is a CEP170-interacting protein that competes with CCDC120 in recruiting CEP170 to SDAs. Furthermore, CCDC120 and CCDC68 are required for centrosome microtubule anchoring. Our findings elucidate the molecular basis for centriole SDA hierarchical assembly and microtubule anchoring in human interphase cells.

LRRC45 is a centrosome linker component required for centrosome cohesion.

During interphase, centrosomes are connected by a proteinaceous linker between the proximal ends of the centrioles, which is important for the centrosomes to function as a single microtubule-organizing center. However, the composition and regulation of centrosomal linker remain largely unknown. Here, we show that LRRC45 is a centrosome linker that localizes at the proximal ends of the centrioles and forms fiber-like structures between them. Depletion of LRRC45 results in centrosome splitting during interphase. Moreover, LRRC45 interacts with both C-Nap1 and rootletin and is phosphorylated by Nek2A at S661 during mitosis. After phosphorylation, both LRRC45 centrosomal localization and fiber-like structures are significantly reduced, which subsequently leads to centrosome separation. Thus, LRRC45 is a critical component of the proteinaceous linker between two centrioles and is required for centrosome cohesion.