We have developed a model of Er/Yb co-doped glasses taking into account upconversion and concentration quenching. We show in this paper that co-doping with Yb does not affect the maximum gain attainable at very high pump power, but significantly enhances the pump efficiency at moderate pump levels.

Novel poly(ρ-phenylene ethynylene) polymers, ANT-OPPE and COU-OPPE, have been prepared, in which anthracene and coumarin sensitizer molecules are covalently attached to the conjugated polymer backbone via a flexible spacer. These polymers show efficient energy transfer from the pendent sensitizer molecule to the PPE backbone, both in dilute solution as well as in an oriented polyethylene matrix. In case of ANT-OPPE, we found that the PPE backbone adapts the orientation of the matrix and is efficiently oriented, while the anthracene moiety remains essentially isotropic, resulting in a state-of-the-art polarizing energy transfer for this system.

Thin layers of poly(dihexylfluorene-co-N-hexylcarbazole) sandwiched between ITO and aluminium electrodes show stable photoluminescence and electro-luminescence at room temperature and ambient atmosphere. I(V) and Electro-luminescence versus voltage curves present a much lower threshold than device made up of poly(dihexylfluorene) homopolymer. When using the copolymer, the barrier height for hole injection is reduced to a value close to 0.17 eV to be compared to 0.83 eV for the homopolymer. This difference in offsets has been confirmed by electrochemical investigations.

A novel family of phasmidic liquid crystals incorporating an oligo(ρ-phenylenevinylene) core was produced. These compounds exhibit blue luminescence in both solution and the solid state. The emission profiles are influenced by the degree of organization in the solid state. The snthesis and liquid-crystalline behavior of these compounds will be discussed. Their photophysical properties, as studied by c.w. photoluminescence excitation, emission spectroscopy, and site selective spectroscopy, as well as their optoelectronic properties will be presented.

Samples of Eu3+ -activated PMMA:PAAc copolymers were prepared in order to investigate their spectroscopic properties. The densities, refractive indices, UV-Visible absorption and emission spectra and fluorescence decay times were obtained experimentally. These data were used in conjunction with Judd-Ofelt theory to calculate the spontaneous emission probabilities and branching ratios, as a function of the europium content. The range of the concentration was 0.1 to 2.5 % mol. Our results are combined with previous information on the optical properties of rare-earth activated polymers in order to get a better understanding of the role played by the Eu3+ ions on the polymerization process in our samples.

The preparation of poly(ρ-phenylene vinylene) (PPV) encapsulated in a mesoporous silica, MCM-41, is reported. In situ polymerization of xylylene bis(tetrahydrothiophenium chloride) yields a highly luminescent, yellow powder with a fluorescence spectrum matching that of unencapsulated PPV. Nitrogen adsorption isotherms show that the pore size of the PPVloaded MCM-41 is significantly smaller than that of empty MCM-41 and a polymer loading of ca. 8% by weight is obtained by thermogravimetric analysis. Photoluminescence data for the encapsulated PPV are presented.

Poly(ρ-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.

We present a study of the effects of blending electroluminescent polymers with platinum (II) octaethylporphyrin (PtOEP). We find that in the case of polymers which are measured to have HOMO and LUMO levels respectively below and above those of the PtOEP, and which have emission spectra overlapping the PtOEP absorption spectra, energy transfer occurs as expected. We find further evidence, in the form of steady state and time-resolved electroluminescence and photoluminescence measurements, which indicates additional transfer of triplet excitons between polymer and porphyrin. Where the polymers have emission spectra overlapping the absorption spectra of PtOEP, but which are measured to have a HOMO or LUMO level between those of the porphyrin, quenching of the photoluminescence efficiency occurs. We propose this is due to charge separation between the porphyrin and the polymer, and show evidence for this in the form of photoinduced absorption measurements.

Langmuir-Blodgett (LB) PPV films of poly(ρ-phenylene vinylene) (PPV) have been obtained using a mixture of a PPV precursor, poly(xylylidene tetrahydrothiophenium chloride) (PTHT), with the sodium salt of dodecylsulfonic acid (DBSA) as the spreading solution. Spincoated films were prepared in order to compare their properties with those of LB films. A large circular dichroism was observed for LB films but not for spin-coated ones. Optical activity of PPV films was characterized by circular dichroism technique, while optical properties were evaluated by optical absorption and luminescence measurements at various temperatures. Overall, the results obtained allowed us to conclude that the layer-by-layer LB process yields a high degree of molecular order in the PPV films with low interchain interaction. Polarized absorption and circular dichroism measurements demonstrate a preferential chain orientation along the dipping direction in the LB processing. The origin of the CD in the PPV-LB can be ascribed to convenient packing of individual monolayers given by the Z-type deposition.

The Judd-Ofelt intensity parameters for f-f transitions of Er3+ ions in PMMA:PAAc copolymer samples were determined from optical absorption measurements and their dependence on the erbium content investigated within the range of 0.1 to 3.0 % mol. The densities, refractive indices and emission spectra have been measured. For our Er-PMMA:PAAc samples an effective radiative transfer between the copolymer host and the erbium ions is observed and discussed.

A good understanding of the electronic states near the band gap of large gap materials is essential for designing phosphors when the energy of exciting radiation exceeds the band gap. This is particularly true when phosphors are designed for application in rare gas discharges with vacuum UV (VUV) radiation. Using density functional ab initio methods (augmented spherical waves and full potential linear muffin-tin orbitals), we have analyzed the nature of host excitations near the band gap energy for a number of complex oxides: LaPO4, AIPO4, BaB2O4, YBO3 and LuBO3 and the common trends in the optical transitions in borates and phosphates and the corresponding binary oxides La2O3, Lu2O3, Y2O3, BaO, B2O3 and P2O5. We have also studied the nature of impurity states of Eu3+ and Pr substituting y3+, in large gap oxides. The studies show how the relative ordering of the one-electron states of activator ions with respect to band states of the host lattice may affect their luminescence properties under host excitation.

There is worldwide interest in the use of fluor materials that emit visible light when exposed to ionizing radiation. Typically, fluors are used as components in high performance electromagnetic calorimeters, down-hole oil well loggers, temperature sensors for equipment with high speed moving parts, and beam positioning systems for large particle accelerators. A candidate fluor should have a large fluorescence efficiency, small reduction in output as a function of exposure, intense visible fluorescence spectrum, large material density, and small prompt fluorescence decay time.

Over the last few years, new fluor materials have been located by organizations such as Oak Ridge National Laboratory, Lawrence Berkeley National Laboratory, and the Department of Defense. These new fluors, such as YAIO3:Ce, YSiO5:Ce, GdSiO5:Ce, Y2O2S doped with Tb, Pr, and Eu, and Gd2O0S doped with Th, Pr, and Eu, show a great deal of promise for use in the applications listed above.

This paper will present a summary of fluor research completed by the authors over the last ten years. These results will be used to establish a fluor characterization program at the Acadiana Research Laboratory (ARL) that will move it to the front of this developing technology.

The multiplet structures of Co2+ doped in ZnO, Co2+ doped in ZnS and Ni2+ doped in ZnS are calculated from first principles using the recently developed discrete variational-multielectron (DV-ME) method, in which the matrix elements of electron-electron repulsion are calculated numerically using the molecular orbitals obtained by cluster calculations. The transition probabilities between the multiplet states are also calculated from first principles using the many-electron wave functions obtained by the DV-ME calculations. The optical spectra of these materials are well reproduced, indicating that the effects of covalency and configuration interactions are properly taken into account in the present calculations.

Porous Polymer/ceramic films were processed via tape casting. Upon doping with luminescent molecules such as platinum(II) octaethylporphine and [Ru(4,7-diphenyl-1,10-phenanthroline)3]C12, the films were used as pressure sensors, yielding a Stern-Volmer constant of A ranging from 0.02 to 0.61. These films also exhibited very fast response times (∼I ms). Tape cast films doped with Rhodamine B were used as temperature sensors under cryogenic conditions. The temperature sensitivity of the doped films increased with increasing Rhodamine B concentration.

Thermal shift and broadening of sharp luminescence lines in three Nd-doped laser garnet crystals, GGG, GSGG, and CYMGG, are investigated in a temperature range of 78 to 600K. These lines are due to the 4F3/2 → 4I9/2 (∼0.94μ) and 4F3/2 → 4I11/2 (∼lμ) transitions. Line widths and positions at different temperatures are reported for the lines of RI→Yl, RI→Y2, R2→Y3, RI→Z5 in GGG:Nd, RI→Y1, RI→Y2, R2→Y1, R2→Y3, RI→Y6, R2→Y6, RI→Z5 in GSGG:Nd,Cr, and R2→Y1, RI→Z5 in CYMGG:Nd,Cr. We observed that all the lines shift to longer wavelengths (red shift) with increasing temperature except for the R1,2 →Z5 lines that shift to shorter wavelength (blue shift) in all the three garnet crystals. For the widths, all the lines become broader with increasing temperature. It was also observed that the line width in the germanium garnet CYMGG is much broader than in GGG and GSGG.

Theoretical calculations at HF/6-31G(d) level were carried out on a series of fully conjugated compounds (4-ethynylbenzaldehyde, β,β-dibromo-4-ethynylstyrene, β,β-Di(4'-formylphenylethynyl)-4-ethynylstyrene and its dimmer) to understand the source of blue emission observed in oligomers of the first and second generation in chloroform solutions. The frontier orbitals are distributed through the framework of the molecules (benzene rings, double and triple bonds and chromophores). Additionally, a configuration interaction approach was applied over β,β-Di(4'-formylphenylethynyl)-4-ethynylstyrene (compound 3) at CIS/6-31G(d) level to modeling excited states and simulate the UV-VIS spectrum experimentally obtained. Calculated transitions corresponded to S0→S1 which are, presumably, responsible for the fluorescence observed.