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Abstract Sm 3 + doped yttrium orthophosphate nanoparticles with porous structure was synthesized via simple co-precipitation method. The structure, the morphology and the elemental composition of the tailored nanoparticles were investigated using transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX). Under the influence of trisodium citrate, Sm 3 + doped YPO 4 phosphor with porous structure could be synthesized. Under our reaction conditions, Sm 3 + doped YPO 4 nanophosphor crystallize in the hexagonal structure, as confirmed by the powder XRD patterns. The formation of porous structure turned out to be an essential step for the peculiar luminescent properties. The porosity undoubtedly enlarges the surface of the semiconductor/air interface, resulting in suppression of the non-radiative recombination channels. The tailored porous yttrium orthophosphate nanoparticles significantly displayed potentiality in the field of optical displays and also demonstrated the applicability in the biological field. Highlights • Utilization of trisodium citrate to control the crystal structure and morphology. • Selective adsorption of Cit 3 − to different facets leads to the growth of porous architecture. • Hexagonal system shows good luminescence property due to its porous structure. [ABSTRACT FROM AUTHOR]

The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law. [ABSTRACT FROM AUTHOR]

Highlights: [•] Photoacoustic spectroscopy of NIR emitting lanthanides in ThO2 is reported for the first time. [•] The nephelauxetic ratio β, bonding parameter b 1/2 and Sinha parameter δ are calculated based on their PA spectra. [•] Effect of lanthanide concentration on the PA spectra of doped thoria was studied. [ABSTRACT FROM AUTHOR]

The BaY2F8 crystals doped with different concentrations of Tm3+ ions were prepared by the temperature gradient technique (TGT). X-ray powder diffraction was applied to analyze the phase. The cracking phenomenon along (010) and (100) planes of the crystals grown by temperature gradient technique was studied on the basis of the structure of BaY2F8 crystals. The absorption spectra were measured and investigated in the ultraviolet-visible and near-infrared ranges at room temperature. Several characteristic absorption bands of Tm3+-doped BaY2F8 crystal were observed. The emission and excitation spectra were obtained and investigated at room temperature and 12 K, showing the characteristic emission peaks of Tm3+ ions. The temperature dependence of Photoluminescence curve was also investigated in the range of 12-296 K. The luminescence intensity of emission bands decreased with increasing temperature, while the effective bandwidth increased. The up-conversion spectrum excited at 650 nm was recorded and up-conversion mechanism was analyzed in detail. The result showed the purple, green and yellow emissions corresponding to 3P1→3F3, 1D2→3H5 and 3P0→1G4 transitions, respectively. [ABSTRACT FROM AUTHOR]

The energy transfer mechanism of two different dyes, C450 as donor and C535 as acceptor incorporated into polymeric matrices, is investigated. The absorption and fluorescence characteristics of C450 and C535 dye-doped polymer modified with ethanol are studied. The results are compared with their respective liquid mixtures. The spectral parameters of C450 and C535 in polymer and the corresponding monomer compositions are obtained. We study the variation of gain for different acceptor concentrations whilst keeping the donor concentration fixed. The gain of acceptor with donor increased and then decreased as the acceptor concentration was increased. Both solid and liquid media showed similar trends. We also study the photobleaching of the dye-doped polymer rod under nitrogen laser excitation. [ABSTRACT FROM AUTHOR]

Abstract: We provide a brief review of our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in two most important dilute nitride systems—Ga(In)NAs grown on GaAs substrates and Ga(Al,In)NP grown on Si and GaP substrates. These results have led to the identification of defect complexes in the alloys, involving intrinsic defects such as AsGa antisites and Gai self-interstitials. They have also shed light on formation mechanisms of the defects and on their role in non-radiative carrier recombination that is harmful to the performance of potential optoelectronic and photonic devices based on these dilute nitrides. [Copyright &y& Elsevier]

The effectiveness of piezoelectric photothermal spectroscopy (PPTS) to investigate surface states and bulk properties of single crystal silicon was demonstrated. PPTS measurements were conducted on p- and n-type, single crystal silicon. A broad peaked signal around 1.18±0.01 eV at room temperature showed the characteristics of slow states present on silicon surface. Another signal bearing a peak around 1.07±0.005 eV at room temperature was due to bulk effect. In the indirect band gap of silicon, the excitation of electrons from valence band to conduction band (so called band-to-band excitation) is not possible without phonon assistance. The PPTS measurements conducted at various temperatures revealed band-to-band and valence band-to-excitons states transition with phonon assistance. The measurements at 4.2 and 110 K resolved four types of phonon participation. A good agreement between theoretical expressions and experimental data substantiated the phonon participation in band-to-band and valence band-to-excitons states transitions. [Copyright &y& Elsevier]

[Display omitted] • Apigenin, Luteolin and Steppogenin were used as sunscreens to study in solution. • Site-selective electron transfer in the excited state is induced by hydrogen bond. • A certain theoretical basis for the application of plant flavonoids in sunscreen cosmetics. • This work clarified the excited state kinetic behavior of Apigenin, Luteolin and Steppogenin in solvent. In this present work, we have successfully designed and investigated three flavonoid sunscreen compounds. Based on steady-state spectroscopy and time-dependent density functional theory (TDDFT), the mechanism of excited state intramolecular proton transfer (ESIPT) of sunscreen compounds was studied. The calculated UV–vis absorption spectra and fluorescence emission spectra are in good agreement with the experimental results in methanol solution. The potential energy curve demonstrates that the ESIPT process can easily occur in the three sunscreen compounds without energy barrier. Therefore, the absorbed excitation energy can get back to the ground state through a non-radiative relaxation process. Light stability tests ensure that the three flavonoids have the potential as sunscreens. This work provides not only an application of the ESIPT process in sunscreen mechanisms, but also a theory basis for the development of novel sunscreen molecules. [ABSTRACT FROM AUTHOR]

In this work, we verified that the newly synthesized octyl urocanate compounds (U1 and U2) can significantly absorb UVB and confirmed their excellent light stability. In addition, we combined the Proton Nuclear Magnetic Resonance (1HNMR) and Time-Dependent Density Functional Theory (TDDFT) calculation methods to clearly explain the UV protection mechanism of U1 and U2. Octyl urocanate can be excited to an excited state after absorbing ultraviolet light in the UVB region. After that, the isomerized molecules at the conical intersection point (CI) between the potential energy surfaces (PESs) of the S 1 and S 0 states, rapidly relax to the ground state from the S 1 excited state in the form of a non-radiative transition. Ultrafast trans -cis photoisomerization can be carried out in a very short time. We found the characteristic peak of cis -U1 from the NMR of trans -U1 after being irradiated by the laser. Therefore, the energy absorbed by U1 and U2 can be quickly consumed through the non-radiative photoisomerization process. Therefore, we believe that octyl urocanate U1 and U2 are very good potential sunscreen molecules that absorb UVB. [Display omitted] • The compounds U1 and U2 with ultraviolet light were prepared by a new octyl urocanate. • U1 and U2 are obtained by esterification on the basis of natural product urocanic acid. • The absorb of U1 and U2 mainly is in the UVB region, and the fluorescence emission intensity is very small. • U1 and U2 can undergo cis -trans isomerization to relax energy after absorbing ultraviolet light. [ABSTRACT FROM AUTHOR]

To resolve the issue of aggregation induced quenching (AIQ), poor adhesion/dispersion on film and fiber, limited dispersability/solubility and non biocompatibility issue; phosphor powder particles are generally casted into solution form. It was found in most cases that lanthanide luminescence and lifetime reduced substantially in aqueous medium and ionic liquid. Deep eutectic solvent (DES) has been found to be an alternate and more efficient solvent for lanthanide luminescence. With similar intention we have synthesized europium type (IV) DES (EuDES) via mechanochemical synthesis employing europium nitrate and urea. Fourier transformed infrared spectroscopy (FTIR) studies confirms that in DES, the Eu3+ ion is surrounded by bidentate nitrate ions and urea is coordinated to europium centre by C O group. There is no water molecule in primary coordination sphere of Eu3+ ion. Interestingly with rigid H-bonding and strong chemical interaction offered by DES; Eu3+ CTB is quenched whereas very high intensity of Eu3+ intra f-f transition appears which was reversal from usual trend. Moreover asymmetry ratio was found to be more than 3 with predominantly high intensity of electric dipole transition (EDT) suggesting very asymmetric environment around Eu3+ in DES. But the distribution of europium was found to be very homogenous with luminescence lifetime of ~3.7 ms and point group symmetry ~ C 6v. Judd-Ofelt analysis suggested very low non-radiative channels present in DES resulting in extremely high quantum yield ~76% and very high color purity of 94.72% which was also assisted by absence of any water molecule as suggested by FTIR measurement. [Display omitted] • Mechanochemical synthesis of type IV europium deep eutectic solvent. • Homogenous distribution of europium in low symmetry. • Unusual high intensity of Eu3+ intra f-f transition. • Lower non-radiative channels and high concentration quenching. • High Quantum yield~76%. [ABSTRACT FROM AUTHOR]

Abstract: The current density and the ideality factor of the non-radiative band-to-impurity recombination current in a p–n diode is calculated analytically in a very good approximation. The usual approximation of multiplying the maximum recombination rate with the width of the depletion layer is very crude. The ideality factor is found to be ⩽2, depending on bias and diffusion voltage. [Copyright &y& Elsevier]