Jorge H.S.K. Monteiro

Determination of Judd-Ofelt Intensity Parameters of Pure Samarium(III) Complexes

This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)3(L)n], with L = H2O, triphenylphosphine oxide (tppo), 2,2′-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H2O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.

Pyrenes, Peropyrenes, and Teropyrenes: Synthesis, Structures, and Photophysical Properties

The design of a relatively simple and efficient method to extend the π-conjugation of readily available aromatics in one-dimension is of significant value. In this paper, pyrenes, peropyrenes, and teropyrenes were synthesized through a double or quadruple benzannulation reaction of alkynes promoted by Brønsted acid. This novel method does not involve cyclodehydrogenation (oxidative aryl-aryl coupling) to arrive at the newly incorporated large arene moieties. All of the target compounds were synthesized in moderate to good yields and were fully characterized with the structures unambiguously confirmed by X-ray crystallography. As expected, photophysical characterization clearly shows increasing red-shifts as a function of extended conjugation within the fused ring systems.

Non-stabilized europium-doped lanthanum oxyfluoride and fluoride nanoparticles well dispersed in thin silica films

Well dispersed non-stabilized lanthanum oxyfluoride and fluoride nanoparticles were prepared in situ in thin silica films from rapid thermal decomposition of lanthanum tris-trifluoroacetate under nitrogen atmosphere. The thin silica films were obtained from sol–gel method and spin-coating. The spectroscopic properties of the non-stabilized nanoparticles as well the nanoparticles dispersed into thin silica films were studied in order to apply the system in future photonic applications such as erbium(III)-doped waveguide amplifiers. The non-stabilized nanoparticles were characterized by XRD, FT-IR, Transmission Electron Microscopy, Confocal Raman Spectroscopy and steady-state and time-resolved Luminescence Spectroscopy and these characterizations were used as a starting point to characterize the nanoparticles dispersed into the films. According to the temperature of the thermal treatments, the non-stabilized nanoparticles may present Eu(III)-doped LaOF in tetragonal and rhombohedral phases as well as a mixed phase of Eu(III)-doped LaF3 and LaOF. The tetragonal LaOF phase has C4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C3v symmetry, consequently tetragonal LaOF presented lower Ω2 values than rhombohedral LaOF. Theoretical calculations of Judd–Ofelt intensity parameters were also performed and were in good agreement with the experimental values. The samples containing the mixed phase of LaF3 and LaOF presented lower values of intensity parameters than pure LaOF phases. The samples containing the mixed phase presented higher values of emission lifetimes and quantum efficiencies. Confocal Raman spectroscopy of these samples complements the luminescence studies and indicates which LaOF phase is present in the mixed phase of LaF3 and LaOF. The rapid thermal decomposition of the precursor tris-trifluoroacetate on thin silica films results in well-dispersed 10 nm nanoparticles. The mixed phase of LaF3 and LaOF phases is also present in thin films. The luminescence of the Eu(III) and Er(III)/Yb(III)-doped LaF3/LaOF nanoparticles containing thin silica films presented broad emission bands suggesting that in the future the systems may be applied as erbium(III)-doped waveguide amplifiers.

Estimating the Donor–Acceptor Distance To Tune the Emission Efficiency of Luminescent Lanthanide Compounds

The influence of the donor-acceptor distance RL on the photophysical properties, including the emission quantum yield, of two europium complexes with the same coordination number, and thus similar microsymmetries, was investigated by spectroscopic and computational methods. K3[Eu(dipicCbz)3] was synthesized using the new ligand dipicCbz and its photophysical properties compared to Cs3[Eu(dipic)3]. We found that a 50% increase in RL from 4.1 to 6.5 Å results in a substantial decrease in the emission efficiency from 24 to 1.8%.

Mn doped AIZS/ZnS nanocrystals: Synthesis and optical properties

In this work, Mn doped AIZS/ZnS (Mn:AIZS/ZnS) nanocrystals (NCs) have been synthesized in an approach using heat-up and drop-wise addition of precursors. On the basis of the characterization of these doped NCs on their optical properties and materials, it is found that: (1) as more Mn atoms are doped into NCs, the doped NCs present photoluminescence (PL) red-shift and quantum yield quenching; (2) the doped NCs possess a short PL lifetime in tens of microseconds and a long PL lifetime in hundreds of microseconds, and the short lived PL is more dominant than the long lived one; and (3) the doped NCs present a reversible PL thermal quenching in a range from room temperature to 170°C. Possible PL mechanisms of these NCs were discussed by analyzing their time-resolved PL spectra and thermal stability.

Photophysical properties of asymmetric and water-soluble dinuclear lanthanide complexes of poly glycol chain functionalized-benzoic acid derivative: experimental and theoretical approaches

New water-soluble lanthanide complexes with a poly glycol chain (–OEtOEtOEtOMe) functionalized benzoic acid derivative ligand were synthesized and photophysically characterized. The results indicate a formation of an asymmetric dinuclear lanthanide complexes. The [Eu2(mee)6(H2O)2] complex shows emission in water solution and it was noted that after 48 h part of the ligands are replaced by water molecules resulting on quenching of the emission and decreasing of lifetimes by O–H oscillators from water molecules. The average Judd–Ofelt intensity parameters were determined experimentally from emission spectra of the europium(III) complex. Additionally, the contribution of each asymmetric europium(III) center to the JO intensity parameters were calculated independently using time resolved spectroscopy and the LUMPAC software helping the proposition of the polyhedral coordination sphere determined by the ground state geometry using the Sparkle/PM3 model. The transfer and back energy transfer rates were also calculated. The values obtained for energy transfer rates are lower than previous values obtained for europium(III) complexes with benzoic acid derivative ligands, indicating the role of the poly glycol chain on photophysical properties of the [Eu2(mee)6(H2O)2] complex.

Lanthanide ion emission in multicolor OLEDs (Ce3+, Pr3+, Tb3+, Dy3+, Tm3+, and white light Eu3+/Tb3+ hybrid systems) and device characterization

Abstract Organic light-emitting diodes are ubiquitous in our daily lives, for cell phone displays, television screens, and visual interfaces. A multicolor display relies on the combination of three colors, namely, red, green, and blue. Eu3+-/Sm3+-based red emissive phosphors were discussed in the previous chapter; here, we will focus on other emission colors in OLEDs achieved by lanthanide ions. We will give a brief introduction of the advantages of OLEDs over other display technologies, followed by a section discussing the techniques used to measure photoluminescence, electroluminescence, and device efficiency. We will then present the emissive profiles of visible-emitting lanthanide ions and recent literature examples of such phosphors.