Evidence of the participation of electronic excited states in the mechanism of positronium formation in substitutional Tb1-xEux(dpm)(3) solid solutions studied by optical and positron annihilation spectroscopies

Positronium formation in the bimary molecular solid solutions Tb1-xEux (dpm)(3) (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the D-5(4) Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.CNPqCNPqFAPEMIGFAPEMIGFAPESPFAPESPRENAMI (National Project)RENAMI (National Project

Highly luminescent Gd2O2S:Er3+,Yb3+ upconversion microcrystals obtained by a time- and energy-saving microwave-assisted solid-state synthesis

Er3+-doped and Er3+,Yb3+-co-doped Gd2O2S are one of the most efficient upconversion (UC) materials available to date. However, preparing lanthanide oxysulfides can be challenging as it requires several hours of heating at > 1000 degrees C in high power furnaces. Nonetheless, in designing a new synthesis technology for UC materials, one should consider that these systems suffer from defect quenching, responsible for significant optical energy losses. In this work, the microwave-assisted solid-state (MASS) synthesis was explored as an alternative to synthesize this class of materials, using two different starting compounds - lanthanide oxides (Ln2O3) and hydroxycarbonates (Ln(OH)CO3), where Ln3+: Gd, Er, Yb. Different Er3+,Yb3+ concentrations were investigated, and the Er3+(5%),Yb3+(5%) and Er3+ (1%),Yb3+ (10%) were shown to give the most intense UC output comparable to commercially available materials. Using Ln(OH)CO3 instead of the more common Ln2O3 for the MASS synthesis contributed to higher UC efficiencies and a more homogeneous Er3+ and especially Yb3+ distribution through the Gd2O2S lattice as verified by luminescence lifetime measurements. These high-quality materials were prepared in a simple two-step synthesis of 50 min and using a domestic microwave oven, leading to a remarkable decrease of 79% in processing time and 93% in energy consumption, making the MASS method suitable to be explored as an alternative synthesis methodology for high performance UC materials.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).</p

POLYPROPYLENE LUMINESCENCE BEHAVIOR THROUGHT STABLE POLYMERIC OPTICAL MARKER

ABSTRACT Researches and publications about luminescent polymers have been developed in the last years due the academic innovation 1 ; however the application is very limited at industrial area. Optical markers processed are few explored due the difficult to process this kind of luminescent materials. The materials used to obtain luminescent polymeric material doped with europium complex was light of the pellets or films is emitted when the materials are exposed in UV lamp (365nm). In this work was possible to process luminescent polymeric:Eu optical marker with properties of thermal and photo stability 2 which can be used as optical marker in extrusion process

Defect to R3+\mathrm{R^{3+}} Energy Transfer: Colour Tuning of Persistent Luminescence in CdSiO3\mathrm{CdSiO_3}

Luminescence from trivalent rare earth (R 3+ : La 3+ –Lu 3+ , excluding Pm 3+ ) ions was studied in the CdSiO 3host. The positions of the R 2+/3+ energy levels in the band structure of CdSiO 3 suggest that the dopingof CdSiO 3 with R 2+ ions is difficult if not impossible. Red, pink, blue, green and close to white persistentluminescence colours were obtained by doping with Pr 3+ , Sm 3+ , Gd 3+ , Tb 3+ and Dy 3+ , respectively. Theefficiency of the defect to R 3+ energy transfer determines if persistent luminescence arises from the 4f–4f, defect or a combination of these two emissions. In contrast to what is observed for Pr 3+ and Tb 3+ ,the defect to R 3+ energy transfer did not give efficient persistent luminescence for Sm 3+ and Dy 3+ ,probably due to high energy losses and/or back transfer from the rare earth to defects. In line with theexperimental observations, the in situ synchrotron radiation XANES spectra indicated the presence ofonly the trivalent Pr 3+ and Tb 3+ species thus excluding the direct R 3+ / R IV oxidation during thecharging process of persistent luminescence. Finally, based on the band gap energy, R 2+/3+ energy levelpositions, trap energies, and other optical and structural properties, the mechanism of persistent luminescence was developed for Pr 3+ doped CdSiO 3 . For practical applications, the CdSiO 3 :R 3+ systemoffers an excellent possibility for colour tuning of persistent luminescence by changing only the R 3+ dopant instead of altering the host as is the case with the Eu 2+ doped materials. Eventually, this will avoid the waste of both intellectual and financial resources

Eu@COK-16, a host sensitized, hybrid luminescent metal-organic framework

A new concept of luminescent host-guest materials was developed by introduction of Eu3+ into COK-16, a HKUST-1 type hybrid metal-organic framework (MOF) with cation exchange properties. In Eu@COK-16, the luminescent ion resides in the pore system of the MOF. The luminescent properties of Eu@COK-16 have been studied based on excitation and emission, allowing analysis of intramolecular energy-transfer processes from the COK-16 host to the exchanged Eu3+ ions. Both, the framework trimesate (BTC) and encapsulated [PW12O40] 3- ions contribute to energy transfer. Since the antenna molecules (BTC) are part of the framework structure and [PW12O40]3- ions only partly occupy one of the three types of cavities in the structure, a large fraction of the pore volume in this host sensitized luminescent MOF remains available for catalysis applications or adsorption of additional sensitizing molecules. The material structure was determined from a combination of elemental analysis, XAS, XRD, electron and luminescence spectroscopy.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available in the Chemical Sciences Article Repository after a 12 month embargo period history: Received 26 March 2014; Accepted 9 May 2014; Accepted Manuscript published 9 May 2014; Advance Article published 30 May 2014; Version of Record published 19 August 2014status: publishe

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE(3+) = Eu(3+), Gd(3+) and Tb(3+)) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H(2)O)(2)], [RE(TLA)(H(2)O)(4)] and [RE(TMA)(H(2)O)(G)], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd(3+)-(BTC) complexes showed that the triplet states (T) of the BTC(3-) anions have energy higher than the main emitting states of the Eu(3+) ((5)D(0)) and Tb(3+) ((5)D(4)), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Omega(2)) of Eu(3+)-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited (5)D(0) and (5)D(4) levels of the Eu(3+) and Tb(3+) ions is discussed. The emission quantum efficiencies (eta) of the (5)D(0) emitting level of the Eu(3+) ion have been also determined. In the case of the Tb(3+) ion, the photoluminescence data show the high emission intensity of the characteristic transitions (5)D(4) -> (7)F(J) (J=0-6), indicating that the BTC ligands are good sensitizers. The RE(3+)-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials. (C) 2009 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Rede de Nanotecnologia Molecular e de Interfaces (RENAMI)Rede de Nanotecnologia Molecular e de Interfaces (RENAMI)Instituto do Milenio de Materiais Complexos (IM<SUP>2</SUP>C)Instituto do Milenio de Materiais Complexos (IM<SUP>2</SUP>C

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide-beta-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)(3)(H(2)O)(2)] and [Tb(acac)(3)(H(2)O)(3)] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln(3+)-beta-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand-Ln(3+) intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the (5)D(4) emitting level of the Tb(3+) ion to the excited triplet state T(1) of the tta ligand coordinated to the Eu(3+) ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)CNPqFAPESPinct-INAMIRENAMIREDE-NANOBIOTEC-BRASI