New Insights To Simulate the Luminescence Properties of Pt(II) Complexes Using Quantum Calculations

The present manuscript reports a thorough quantum investigation on the luminescence properties of three monoplatinum­(II) complexes. First, the simulated bond lengths at the ground state are compared to the observed ones, and the simulated electronic transitions are compared to the reported ones in the literature in order to assess our methodology. In a second time we show that geometries from the first triplet excited state are similar to the ground state ones. Simulations of the phosphorescence spectra from the first triplet excited states have been performed taking into account the vibronic coupling effects together with mode-mixing (Dushinsky) and solvent effects. Our simulations are compared with the observed ones already reported in the literature and are in good agreement. The calculations demonstrate that the normal modes of low energy are of great importance on the phosphorescence signature. When temperature effects are taken into account, the simulated phosphorescence spectra are drastically improved. An analysis of the computational time shows that the vibronic coupling simulation is cost-effective and thus can be extended to treat large transition metal complexes. In addition to the intrinsic importance of the investigated targets, this work provides a robust method to simulate phosphorescence spectra and to increase the duality experiment-theory

Two-Step Design of a Single-Doped White Phosphor with High Color Rendering

A strategy to design step by step an inorganic single-doped white phosphor is demonstrated. The method consists in tuning different contributions of the emission by successively controlling the chemical compositions of the solid solution or nanosegregated host matrix and the oxidation states of the single dopant. We use this approach to design a white phosphor Na₄CaMgSc₄Si₁₀O₃₀:Eu with excellent color rendering (CRI > 90) that is similar to common mixed-phosphor light sources but for a single-phase. We show that this methodology can also be extended to other phosphors for use in diverse applications such as biomedicine or telecommunications

Exploring Optical and Vibrational Properties of the Uranium Carbonate Andersonite with Spectroscopy and First-Principles Calculations

Original periodic first-principles calculations based on the generalized gradient approximation combined with several analyses in microspectroscopy are presented for a hydrated uranium carbonate crystal, andersonite, possessing a specific channel structure. Infrared and ultraviolet–visible absorption, Raman scattering, and steady-state and time-resolved photoluminescence spectroscopy are used to address the atomic vibrations of water, uranyl, and carbonate ions, to determine the fluorescence decay time (around 220 μs) and to estimate the amplitude of the optical gap (close to 3 eV). The role of structural water for andersonite stability is discussed by also performing calculations on a dehydrated model structure. Experiments and calculations address both the intrachannel and extra channel possibilities for the water molecules. The current research is a detailed study of a water-containing channel uranium system using a combined infrared/Raman treatment coupled with density functional theory calculation, providing new physical insight into the spectroscopic understanding of these channels

Structural and Spectroscopic Investigations of Two [Cu₄X₆]^2– (X = Cl^–, Br^–) Clusters: A Joint Theoretical and Experimental Work

Herein we report a joint experimental and theoretical investigation on two tetranuclear Cu­(I) clusters stabilized by halide ligands. These clusters are of high interest due to their spectroscopic and optical properties, more precisely both clusters exhibit thermochromism. The compounds synthesized by the hydrothermal method have been characterized by single-crystal X-ray diffraction, UV–visible spectroscopy and quantum calculations. Modeled structures have been investigated by means of DFT and TD-DFT methods. Anharmonic computations have been performed to better achieve the vibrational investigation. Computations of the triplet excited states permit us to get more insights into the structure and electronic structure of the excited states responsible for the luminescence properties. Calculations are in agreement with the observed phosphorescence wavelengths

Luminescence and Location of Gd³⁺ or Tb³⁺ Ions in Perovskite-Type LaScO₃

The luminescence properties of Gd³⁺ or Tb³⁺ ions at La and Sc sites were investigated in LaScO₃ with a distorted perovskite-type structure (ABO₃). Although the luminescence of lanthanide ions located at B sites is not common and has not been examined in detail, Gd³⁺ or Tb³⁺ luminescence from B sites and A sites is clearly observed in Gd³⁺- or Tb³⁺-doped LaScO₃. The differences in the luminescence characteristics concern peak positions, peak shapes, and decay time, which are all influenced by the crystal field and the site symmetry. The UV luminescence of Gd³⁺ at B sites shows a red shift compared to Gd³⁺ at A sites, and the green luminescence of Tb³⁺ at B sites contrasts with the blue-violet and green luminescence of Tb³⁺ at A sites. The decay time of the luminescence from B sites is systematically longer than that from A sites in both the Gd³⁺ and Tb³⁺ cases

Considerations for spectroscopy of liquid-exfoliated 2D materials: emerging photoluminescence of N-methyl-2-pyrrolidone

N-methyl-2-pyrrolidone (NMP) has been shown to be the most effective solvent for liquid phase exfoliation and dispersion of a range of 2D materials including graphene, molybdenum disulphide (MoS2) and black phosphorus. However, NMP is also known to be susceptible to sonochemical degradation during exfoliation. We report that this degradation gives rise to strong visible photoluminescence of NMP. Sonochemical modifcation is shown to infuence exfoliation of layered materials in NMP and the optical absorbance of the solvent in the dispersion. The emerging optical properties of the degraded solvent present challenges for spectroscopy of nanomaterial dispersions; most notably the possibility of observing solvent photoluminescence in the spectra of 2D materials such as MoS2, highlighting the need for stable solvents and exfoliation processes to minimise the infuence of solvent degradation on the properties of liquid-exfoliated 2D materials

Color Control in Coaxial Two-Luminophore Nanowires

We report a general and simple approach to take control of the color of light-emitting two-luminophore hybrid nanowires (NWs). Our strategy is based on the spatial control at the nanoscale (coaxial geometry) and the spectral selection of the two kinds of luminophores in order to restrict complex charge and energy transfers. Thus, it is possible to control the color of the photoluminescence (PL) as an interpolation of the CIE (Commission Internationale de l’Eclairage) coordinates of each luminophore. For this purpose, we selected a green-emitting semiconducting polymer and a red-emitting hexanuclear metal cluster compound, (<i>n</i>-Bu₄N)₂Mo₆Br₈F₆, dispersed in a poly(methyl-methacrylate) (PMMA) matrix. The great potential and the versatility of this strategy have been demonstrated for two configurations. First, a yellow PL with a continuous change along the nanowire has been evidenced when the proportion of the PPV shell <i>versus</i> the nanocomposite core, that is, the green/red volumic ratio, progressively shifts from 1:2 to 1:5. Second, an extremely abrupt change in the PL color with red-green-yellow segments has been achieved. A simple model corroborates the effectiveness of this strategy. PL excitation and time-resolved experiments also confirm that no significant charge and energy transfers are involved. The two-luminophore hybrid nanowires may find widespread nanophotonic applications in multicolor emitting sources, lasers and chemical and biological sensors

Luminescence Enhancement of Pyrene/Dispersant Nanoarrays Driven by the Nanoscale Spatial Effect on Mixing

This work presents a simple method to generate ordered chromophore/dispersant nanoarrays through a pore-filling process for a nanoporous polymer template to enhance chromophore luminescence. Fluorescence results combining with the morphological evolution examined by scanning probe microscopy reveal that the enhanced luminescence intensity reaches the maximum intensity as the nanopores of the template are completely filled by the chromophore/dispersant mixture. The variation is attributed to nanoscale spatial effect on the enhanced mixing efficiency of chromophore and dispersant, that is, the alleviation of self-quenching problem, as evidenced by the results of attenuated total reflection Fourier transform IR spectroscopy combining with grazing incident wide-angle X-ray diffraction. The enhanced luminescence of the chromophore/dispersant nanoarrays driven by the nanoscale spatial effect is highly promising for use in designing luminescent nanodevices