Photoluminescence Phenomena Research Articles

Thermoswitchable emission and coloration of a composite material containing a europium(iii) complex and a fluoran dye

A multifunctional composite film that exhibited thermoresponsive absorption and emission was fabricated using a thermochromic fluoran dye, its developer, and a luminescent europium(III) complex. The emissions from and coloration of this composite film could be reversibly changed and maintained via the thermochromic reaction taking place within the fluoran dye–developer system. The coloration and decoloration of the composite film were caused by thermoresponsive control of the nanoscale aggregation of structures of the fluoran dye and its developer, whose molecular structure consisted of a long alkyl chain. The control of the phenomenon of photoluminescence could also be achieved via thermochromism, which was induced by intermolecular energy transfer from the Eu(III) ions in the excited state to the fluoran dye.

Thermo-switchable Imaging Medium Achieving Both Emissive Reflective Modes

A multifunctional composite film that exhibited thermoresponsive absorption and emission was fabricated using a thermochromic leuco dye, its developer, and a luminescent Europium(III) complex. The emissions from and coloration of this composite film could be reversibly changed and maintained via the thermochromic reaction taking placing within the leuco dyedeveloper system. The coloration and decoloration of the composite film were caused by thermoresponsive control of the nanoscale aggregation of structures of the leuco dye and its developer, whose molecular structure consisted of a long alkyl chain. The control of the phenomenon of photoluminescence could also be achieved via thermochromism, which was induced by intermolecular energy transfers from the Eu(III) ions in the excited states to the leuco dye.

Structural XANES characterization of Ca0.99Sm0.01TiO3 perovskite and correlation with photoluminescence emission

In this work, CaTiO3:Sm (CT:Sm) were prepared by a soft chemical processing at different annealing temperatures starting with a disordered structure and reaching an ordered one, with the propose to understand the relationship between structural order–disorder and photoluminescence emission. The samples were characterized by titanium K-edge, Titanium LII and LIII-edge XANES, electron paramagnetic resonance (EPR) and photoluminescence (PL) measurements. XANES results clearly point the presence of local distortion in [TiO6] octahedral clusters until the crystallization was completed. The interactions of the network clusters that form the CT:Sm structures provides favorable structural and electronic conditions for the appearance of PL phenomena.

Energy Transfer in Na6Pb4(SO4)6Cl2: X, Y (X = Ce or Eu; Y= Dy or Tb)

Polycrystalline new Na6Pb4(SO4)6Cl2:(Ce3+; Ce3+ →Dy3+; Ce3+ →Tb3+ and Eu2+ →Dy3+) halosulphate inorganic phosphors were synthesized by solid state diffusion method. The effects of Dy3+ and Tb3+co-doping on the photoluminescence (PL) characteristics of the phosphors have been studied. In Na6Pb4(SO4)6Cl2, Ce3+ emission is observed at 340 nm due to 5d → 4f transition of Ce3+ ion. A strong PL emission of Dy3+ ions is observed at 475 and 575 nm in Na6Pb4(SO4)6Cl2: Ce, Dy phosphor, while Tb3+ green color emission is also observed at 550 nm in Ce3+ → Tb3+ energy transfer. The host is also suitable for sufficient Eu2+ →Dy3+ energy transfer. This paper reports that Na6Pb4(SO4)6Cl2 inorganic material is most suitable for photoluminescence phenomena and energy transfer mechanism. Keywords: Energy transfer, halosulphate, inorganic phosphor, photoluminescence, rare earths, solid state diffusion

Effect of Sb<sub>2</sub>O<sub>3</sub> addition on photoluminescence properties of zinc phosphate and borate glasses

Trivalent cation oxides were added to zinc phosphate glasses by conventional melt-quenching technique to dope excess electrons in order to create donor electrons easily excited by the incident light, in specific Ga2O3 and Sb2O3. By exciting 200 and 250 nm light, the glasses containing Sb2O3 emitted visible light, while no emission from those containing Ga2O3 could be observable.The intensity of emission light depended upon Sb2O3 concentration, and 0.3–1.0 mol % Sb2O3 addition was most effective for the emission, and concentration quenching was seen in over 5 mol % Sb2O3 addition. With respect to necessity of the presence of ZnO was explored by replacing ZnO by CaO and BaO. Even by changing of ZnO by CaO and BaO, the emission intensity was not influenced. Further, we used borate glasses instead of phosphate glasses. Since only weak emission was obtained from borate glasses, P2O5 can be considered to be indispensable for photoluminescence (PL) phenomena.

ChemInform Abstract: Recent Progress in the Theoretical Studies of Structure, Function, and Reaction of Biological Molecules

AbstractReview: 44 refs.

Recent Progress in the Theoretical Studies of Structure, Function, and Reaction of Biological Molecules

Essential biomolecular functions often involve electron-related events such as chemical reactions and photoluminescence phenomena. Theoretical description of such electronic processes requires the use of quantum mechanics (QM), but the number of atoms that can be handled with QM is usually smaller than the number of atoms present in a single protein. A reasonable strategy is therefore to give priority to a few tens or hundreds of atoms in the system and deal with them quantum mechanically. Lower-priority atoms influence the event occurring in the higher-priority area; therefore, their effect should also be taken into account. Under these circumstances, a reasonable approach is to apply two or more different theoretical methods to differently prioritized subsystems. QM can be combined, for example, with less accurate yet much less demanding molecular mechanics (MM). Our own N-layered integrated molecular orbital and molecular mechanics (ONIOM) method allows for such hybrid calculations, and our group has been applying it to a wide range of biology-related problems. In this paper, we briefly explain the theoretical background and the procedure for the theoretical investigation of biological systems. Subsequently, we provide an overview of some of our recent studies of metalloenzymes and photobiology-related problems.

Density functional investigation of structural, electronic and optical properties of Ge-doped ZnO

Recent experiments reported fascinating phenomenon of photoluminescence (PL) blueshift in Ge-doped ZnO. To understand it, we examined the structural, electronic and optical properties of Ge-doped ZnO (ZnO:Ge) systematically by means of density functional theory calculations. Our results show that Ge atoms tend to cluster in heavily doped ZnO. Ge clusters can limit the conductivity of doped ZnO but reinforce the near-band-edge emission. The substitutional Ge for Zn leads to Fermi level pinning in the conduction band, which indicates Ge-doped ZnO is of n-type conductivity character. It is found that the delocalized Ge 4s states hybridize with conduction band bottom, and is dominant in the region near the Fermi level, suggesting that Ge-4s states provides major free carriers in ZnO:Ge crystal. The observed blueshift of PL in Ge-doped ZnO originates from the electron transition energy from the valence band to the empty levels above Fermi level larger than the gap of undoped ZnO. The electron transition between the gap states induced by oxygen vacancy and conduction band minimum may be the origin of the new PL peak at 590 nm.

Origin of UV Sensitivity of SiON Film and Bidirectional UV Trimming of SiON Microring Resonator

We discovered a photoluminescence phenomenon of SiON waveguide by the UV irradiation and investigated the luminescence spectrum by a conventional microscope and diffraction grating spectroscopy. It was shown from these measurements that the defect created by UV irradiation causes the UV sensitivity of SiON film after thermal annealing. Next, we measured the spectrum change of a microring resonator with SiON core via single point long time UV irradiation and multi point UV irradiation. As a result, we demonstrated a selective UV trimming of microring resonator combining thermal annealing and multi point UV irradiation.

Facile hydrothermal synthesis of uniform 3D γ‐AlOOH architectures assembled by nanosheets

AbstractUniform γ‐AlOOH architectures assembled by nanosheets were successfully synthesized in the mixture of deinonized water and dimethyl sulfoxide (DMSO) at 180 °C. The structure and morphology of products were characterized by X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The products displayed 3D microstructures with its length of 1 μm and diameter of 400‐500 nm. The obtained γ‐AlOOH structures exhibited large Brunauer‐Emmett‐Teller (BET) surface area of 216.5 m2/g and pore size of 3.7 nm. The formation mechanism of 3D γ‐AlOOH architectures was also discussed based on the experimental results. Furthermore, the γ‐AlOOH architectures exhibited preliminary photoluminescence (PL) phenomenon with a strong peak at 323 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On the photoluminescence behavior of samarium-doped strontium titanate nanostructures under UV light. A structural and electronic understanding

A combined experimental and theoretical investigation on the photoluminescence properties of SrTiO(3) (ST) and SrSm(0.01)Ti(0.99)O(3) (ST_Sm) nanostructures is presented in this work. The nanocrystalline powders were prepared by the polymeric precursor method, and the order-disorder behavior of this material was investigated by means of X-ray diffraction (XRD), spectral absorbance (UV-vis), transmission electron microscopy (TEM) images, electron paramagnetic resonance (EPR) and photoluminescence (PL) experimental techniques. The decrease in the broad PL emission band of ST and ST_Sm powders measured at room temperature indicates an increase in the structural order as the annealing temperature increases, i.e. characteristic samarium peaks intensify as the structural order increases in ST_Sm samples. The interactions of the network clusters that form the ST and ST_Sm structures were evaluated by means of the ab initio periodic method at the density functional theory (DFT) level with the hybrid nonlocal B3LYP approximation. The symmetry-breaking process that leads to the presence of non-ideal [TiO(6)] and [SrO(12)] clusters, as well as the relationship between these clusters, provides favorable structural and electronic conditions for the appearance of PL phenomena.

Photoluminescence Phenomena of Functional Dopant Doped Soluble Polypyrroles in Organic Solvents

We have investigated the photoluminescence (PL) phenomena of functional dopant doped polypyrroles (Ppy-DEHS, Ppy-BNS) in organic solvents with various conditions. From the results of UV-Vis. and PL spectra, we found that the change in polymer chain conformation from expanded to coil-like structure resulted in blue-shifted emission and reduced PL intensity. Addition of small amount of non-polar solvent to polar solvent media did not influence the shapes of PL curves but reduced the PL intensity under photo-excitation at 380 nm.

The role of oxygen vacancy in the photoluminescence property at room temperature of the CaTiO3

In this paper, electron paramagnetic resonance, photoluminescence (PL) emission, and quantum mechanical calculations were used to observe and understand the structural order-disorder of CaTiO3, paying special attention to the role of oxygen vacancy. The PL phenomenon at room temperature of CaTiO3 is directly influenced by the presence of oxygen vacancies that yield structural order-disorder. These oxygen vacancies bonded at Ti and/or Ca induce new electronic states inside the band gap. Ordered and disordered CaTiO3 was obtained by the polymeric precursor method.

Electron spin resonance and photoluminescence in pyrolytic silicon nitride films irradiated with argon and molecular ions

The photoluminescence and electron spin resonance phenomena are studied at room temperature for pyrolytic silicon nitride films irradiated with argon ions or molecular nitrogen ions and annealed at temperatures in the range 500–1100°C. The absorption spectrum suggests that the broad photoluminescence band at 400–600 nm is due to electron transitions between the band tails. The low-dose irradiation with argon ions slightly reduces the photoluminescence intensity, whereas the high-dose irradiation followed by annealing at 800–900°C can induce a more than twofold increase in the intensity. At the same time, irradiation with nitrogen ions profoundly suppresses the integrated photoluminescence intensity that decreases by more than an order of magnitude. A correlation between the changes in the photoluminescence intensity and the amplitude of the ESR spectra on annealing of the silicon nitride films is observed.

Microporous Lanthanide Metal-Organic Frameworks Containing Coordinatively Linked Interpenetration: Syntheses, Gas Adsorption Studies, Thermal Stability Analysis, and Photoluminescence Investigation

Under solvothermal conditions, the reactions of trigonal-planar ligand, TATB (4,4',4''-s-triazine-2,4,6-triyl-tribenzoate) with Dy(NO(3))(3), Er(NO(3))(3), Y(NO(3))(3), Yb(NO(3))(3), gave rise to four microporous lanthanide metal-organic frameworks (MOFs), designated as PCN-17 (Dy), PCN-17 (Er), PCN-17 (Y), and PCN-17 (Yb), respectively. The four porous MOFs are isostructural, with their crystal unit parameters shrinking in the order of PCN-17 (Dy), PCN-17 (Y), PCN-17 (Er), and PCN-17 (Yb), which also reflects the lanthanides' contraction trend. All of them adopt the novel square-planar Ln(4)(mu(4)-H(2)O) cluster as the secondary building unit and contain coordinatively linked doubly interpenetrated (8,3)-connected nets. In addition to exhibiting interesting photoluminescence phenomena, the coordinatively linked interpenetration restricts the pore sizes and affords them selective adsorption of H(2) and O(2) over N(2) and CO, as well as renders them with high thermal stability of 500-550 degrees C as demonstrated from TGA profiles.

Preparation of functional metal nanoparticles embedded mullite composite powders by solid solution reduction

The mullite composite powders with embedded Fe and Ge nanoparticles were individually prepared through the reduction of Al5.4Fe0.6Si2O13 and Al12Si3.75Ge0.25O26 solid solution. The complete reduction of Fe3+ cation in solid solution is realized by hydrogen at 1200°C for 1 h. The magnetic properties of composite powders such as hysteresis loops and magnetization versus temperature were measured using SQUID. The Fe nanoparticles with the particle size around 10 nm embedded in mullite grain show the superparamagnetic behavior with the blocking temperature around 50 K. The mullite composite powders with Ge nanoparticles have strong room temperature photoluminescence (PL) at 561, 610, 676, 713 and 787 nm, respectively. The highest photoluminescence intensity was observed in the sample reduced at 500°C for 3 h. Based on the analysis of XPS and Raman spectra, it is clear that the PL phenomenon is derived from the formation of embedded Ge clusters with the average size of around 1-2 nm in mullite composite powders. It is proved that the multi-functional mullite nanocomposites with functional metal nanoparticles can be prepared through the selective reduction of designed solid solutions.

Structure and photoluminescence of mullite-Ge nanocomposite

Al12Si3.75Ge0.25O26 ceramic powder was prepared by sol-gel method using Al(NO3)3, Si(OC2H5)4 and Cl3GeCH2-CH2COOH as precursors. The structural formation of Al12Si3.75Ge0.25O26 ceramic powder was analyzed by XRD. After reduction by flowing H2/Ar mixture gas, strong room temperature photoluminescence (PL) can be observed at 565 nm, 613 nm, 682 nm, 731 nm and 777 nm, respectively. The PL intensity scarcely depends on the reduction temperature and duration, while the sample reduced at 500℃ for 3 hours has the highest PL intensity. Before and after reduction at 500℃, the volume of unit cell of mullite solid solution decreases to 0.4699 A^3. Based on the analysis of XPS and Raman spectra, it can be approved that the PL phenomenon at room temperature is caused by the embedded Ge nanoparticles with the average size of about 1.95 nm.

Current improvement of porous silicon photovoltaic devices by using double layer porous silicon structure: applicable in porous silicon solar cells

The photoluminescence (PL) phenomena of porous silicon (PS) samples with different etching times were examined to find out a relationship between PL emission energy (experimental value of PS band gap energy) and the etching time for fabrication of double (two) layer porous silicon sample on one silicon substrate. The dependence of PL Peak energy with etching time was discussed. A double layer PS structure was formed by using two electrochemical reactions with different etching times of 20 and 10 min, respectively. The photovoltaic (PV) properties of mono layer and double layer porous silicon PV devices were examined and compared. The main result is the enhanced short-circuit current (Isc) of double layer PS structure compared to monolayer ones.

Photoluminescence from colloidal silver nanoparticles

Highly luminescent singles of Ag sol with gradual changes were detected when adjusting the granularity and concentration of particles. It can be deduced that these Ag sols, composed of a large amount of silver nanoparticles and clusters, may have their surface energy bands alterable, which might be caused by the interactions between particles. A model that describes the shift of energy band is proposed, and it can be understood as the hybridization of elementary plasmons when interactions occur between particles. Besides, both hybridization and absorption-rescattering mechanisms were proposed to explain the changeable phenomena of photoluminescence with different concentrations.

Phosphorescent Organic Light-emitting Devices: Triplet Energy Management

This review paper describes the device performance and light-emission mechanism for phosphorescent organic light-emitting devices (OLEDs), as well as energy transfer processes in phosphorescent host-guest systems. The characteristics of a green phosphorescent OLED, with representative guest and host materials, are presented and its working mechanism is discussed. To improve the emission efficiency, the confinement of triplet energy in the guest molecules is demonstrated for a blue phosphorescent OLED. Photoluminescence phenomena in phosphorescent host-guest systems are presented, and the energy transfers between the host and guest molecules are also discussed.