TY - JOUR A1 - Tiseanu, Carmen A1 - Parvulescu, Vasile I. A1 - Boutonnet, Magali A1 - Cojocaru, Bogdan A1 - Primus, Philipp A. A1 - Teodorescu, Cristian M. A1 - Solans, Conchita A1 - Sanchez Dominguez, Margarita T1 - Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Pure and europium (Eu3+) doped cerium dioxide (CeO2) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce4+ sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce4+ relative to Ce3+ ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed. Y1 - 2011 U6 - https://doi.org/10.1039/c1cp21135h SN - 1463-9076 VL - 13 IS - 38 SP - 17135 EP - 17145 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Cojocaru, Bogdan A1 - Parvulescu, Vasile I. A1 - Sanchez-Dominguez, Margarita A1 - Primus, Philipp A. A1 - Boutonnet, Magali T1 - Order and disorder effects in nano-ZrO2 investigated by micro-Raman and spectrally and temporarily resolved photoluminescence JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Pure and europium (Eu3+) doped ZrO2 synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm(-1) the correlation between the phonon spectra of ZrO2 and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu3+ f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500 degrees C, the overall Eu3+ emission is dominated by Eu3+ located in tetragonal symmetry lattice sites with a crystal-field splitting of the D-5(0)-F-7(1) emission of 20 cm(-1). Annealing of ZrO2 at 1000 degrees C leads to a superposition of Eu3+ emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm(-1) for the D-5(0)-F-7(1) transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu3+ doped ZrO2 samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases. Y1 - 2012 U6 - https://doi.org/10.1039/c2cp41946g SN - 1463-9076 VL - 14 IS - 37 SP - 12970 EP - 12981 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Lorenz-Fonfria, Victor A. A1 - Parvulescu, Vasile Ion A1 - Geßner, Andre A1 - Kumke, Michael Uwe T1 - Photoluminescence study of terbium-exchanged ultrastable Y zeolites: Number of species, photoluminescence decays and decay-associated spectra Y1 - 2008 UR - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=JAPIAU000104000003033530000001&idtype=cvips&doi=10.1063/1.2966304&prog=normal U6 - https://doi.org/10.1063/1.2966304 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Kumke, Michael Uwe A1 - Parvulescu, Vasile Ion A1 - Geßner, Andre A1 - Gagea, Bogdan A1 - Martens, Johan T1 - Europium(3+) : an efficient luminescence probe for the Si to Al ratio and silylation effect in the microporous- mesoporous Zeogrid materials Y1 - 2008 UR - http://pubs.acs.org/doi/pdf/10.1021/jp711337h U6 - https://doi.org/10.1021/Jp711337h ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Parvulescu, Vasile Ion A1 - Cojocaru, Bogdan A1 - Lorenz-Fonfria, Victor A. A1 - Kumke, Michael Uwe A1 - Gessner, Andre A1 - Enculescu, Ion T1 - Polymer-microporous host interactions probed by photoluminescence spectroscopy N2 - Zeolites NaY and ZSM-5 were used as hosts for styrene polymerization after ion-exchange with europium ions. The parent and hybrid, polystyrene coated Eu-NaY (Eu-NaY/PS) and Eu-ZSM-5 (Eu-ZSM-5/PS) zeolites were investigated by using thermal analysis, SEM, PXRD, FT-IR, DR-UV/Vis, steady state and time-resolved photoluminescence spectroscopy. FT-IR spectra evidenced for the interaction between the zeolitic hosts and polystyrene while the PXRD spectra supported for the presence of the polymer inside the channels/pores of Eu-NaY/PS and Eu-ZSM-5/PS materials. The optical properties of Eu-NaY/PS and Eu-ZSM-5/PS were significantly changed relative to those of the parent zeolites, giving further evidence for the presence of polymer inside zeolites. An interesting case is presented by NaY zeolite: following styrene polymerization, the polymer interacted selectively with one of the two main species co-existing inside zeolite while for ZSM-5 a similar effect was not observed. Y1 - 2010 UR - http://www.rsc.org/Publishing/Journals/CP/index.asp U6 - https://doi.org/10.1039/B922591a SN - 1463-9076 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Parvulescu, Vasile A1 - Parvulescu, Victoria A1 - Cotoi, Elena A1 - Gessner, Andre A1 - Kumke, Michael Uwe A1 - Simon, Simion A1 - Vasiliu, Florin T1 - Structural and photoluminescence characterization of mesoporous silicon-phosphates N2 - Two different types of mesoporous silicon-phosphate supports using different surfactants (a mixture of (CH3)(3)C13H27NBr with an organophosphorus coupling molecule (HO-PO(i-C3H7)(2)) and with a co-surfactant ((C2H5)(3)(C6H5)PCl), respectively) were synthesized. Trivalent europium (Eu) ions were immobilized via ion-exchange on these supports. The resulting materials were characterized using nitrogen adsorption isotherms at -196 degrees C, thermogravimetric analysis, SEM, TEM, FT-IR, PXRD, CP/MAS. (HSi)-H-1-Si-29 and P-31 NMR, DR-UV-vis as well as steady- state and time-resolved photoluminescence spectroscopy. The results evidenced that the co-polymerization of silicon and phosphorous yielded a unique morphology in these materials. Following calcination at 450 and 900 degrees C europium- exchanged silicon-phosphates with great surface area (BET=600-705 m(2) g(-1)) and 3.4 nm sized mesopores were obtained. The differences among the optical properties of the non-calcined europium materials such as the emission lifetimes, local environment at the europium sites or the relative contribution of the upper excited levels to the total photoluminescence were assigned to the surfactants used in the synthesis. Calcination of the silicon-phosphates at higher temperatures than 450 degrees C did not induce major changes in the structural properties: in contrast, photoluminescence properties of europium were markedly improved in terms of intensity and average lifetime. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/10106030 U6 - https://doi.org/10.1016/j.jphotochem.2010.07.015 SN - 1010-6030 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Pârvulescu, Victor I. A1 - Kumke, Michael Uwe A1 - Dobroiu, Svako A1 - Geßner, André A1 - Simon, Simion T1 - Effects of support and ligand on the photoluminescence properties of siliceous grafted europium complexes N2 - Europium ions were introduced in SiO2 and MCM-41 via two different pathways: (1) grafting the europium complexes with two alkoxide structures, 3-(2-imidazolin-1-yl)-propyl-triethoxysilane (IPTES) and aminopropyltrimethoxysilane (APTMS), and (2) functionalization of the SiO2 support with silicon 4- carboxylbutyltriethoxide followed by subsequent addition of the europium ions. The new materials were characterized using nitrogen adsorption isotherms at -196 degrees C, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared, NMR, DR-UV-vis, steady-state emission and excitation, and time-resolved photoluminescence spectroscopy. Spectral changes found in the time-resolved photoluminscence spectra strongly point to the distribution of europium ions on a range of environments in both SiO2 and MCM-41 supports. The average europium photoluminescence lifetimes decrease within the order: Eu3+-IPTES/SiO2 (550 mu s) > Eu3+-APTMS/SiO2 (425 mu s) > Eu3+-APTMS/MCM-41 (370 mu s) > Eu3+-IPTES/MCM-41 (320 mu s) > Eu3+-CABES/SiO2 (240 mu s). The photoluminescence quantum efficiency has the largest value, of 22%, for Eu3+-IPTES/SiO2, while the most reduced value, of 9%, was measured for Eu3+-CABES/SiO2. Y1 - 2009 UR - http://pubs.acs.org/journal/jpccck U6 - https://doi.org/10.1021/Jp808411e SN - 1932-7447 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Kumke, Michael Uwe A1 - Pârvulescu, Vasile Ion A1 - Martens, Johan T1 - Species-related luminescence-structure relationships in europium-exchanged mesoporous material N2 - Europium exchanged into a mesoporous material (Zeotile-1) was extensively characterized with respect to the Si/ Al ratio and surface silylation by using time-resolved emission spectroscopy. Qualitative as well as quantitative details of the europium species-related luminescence-structure relationships were obtained and discussed such as the decay associated spectra, local distortion and structure of the bonding environment, crystal-field strength, radiative relaxation rates, and the quantum efficiency. Thus, two europium species were found in the parent as well as in the silylated materials: one species located on the internal surface and the second inside the 2-2.5 nm pores. The species located on the internal surface is characterized by photoluminescence decay times of 105 mu s vinyl > hexadecyl > parent for ZSM-5, hexadecyl a parts per thousand phenyl a parts per thousand vinyl > parent for MOR and hexadecyl > phenyl a parts per thousand vinyl > a parts per thousand parent for BEA zeolites, respectively. Y1 - 2009 UR - http://www.springerlink.com/content/100190 U6 - https://doi.org/10.1007/s10854-008-9597-1 SN - 0957-4522 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Frunza, L. A1 - Kumke, Michael Uwe T1 - Time-resolved photoluminescence analysis of distribution and migration of terbium ions in zeolites X N2 - The photoluminescence (PL) dynamics of terbium-exchanged zeolites X was investigated upon laser excitation at 355 nm. The results evidenced the presence of at least two terbium main environments with PL lifetimes varying between 391-411 and 753-770 mus. The two-site nature of terbium distribution in zeolites X permitted a quantitative analysis of the migration process of terbium ions inside the pores and cavities upon dehydration in air at 200 degreesC. Besides the increase of the PL lifetimes with about 30% and 80% compared to those of the hydrated zeolite, a fraction of almost 30% of terbium ions was estimated to migrate from the supercages to the neighboring sodalites or hexagonal prisms. Our results evidenced for the first time the capability of time-resolved luminescence spectroscopy in quantitatively tracking for the intrazeolitic migration of lanthanides. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Geßner, Andre A1 - Kumke, Michael Uwe A1 - Gagea, Bogdan A1 - Parvulescu, Vasile Ion A1 - Martens, Johan T1 - Photoluminescence spectra and dynamics of lanthanide-doped microporous materials N2 - A series of terbium- and europium-exchanged microporous-mesoporous zeolite Socony Mobil Five (MFI)-type materials such as Zeotile-1 and Zeogrid with varying Si/Al ratios was investigated using FTIR, PXRD, adsorption- desorption isotherms of N-2 at 77 K and time-resolved luminescence spectroscopy. Silylation of the lanthanides-exchanged Zeotile-1 and Zeogrid with hexadecyl trimethoxysilanes via post-synthesis grafting was also studied. The results showed that the lanthanide's photoluminescence spectra and decays were modified due to silylation. The different silylation effects in Zeotile-1 and Zeogrid were correlated with the textural properties of the investigated materials. (C) 2007 Elsevier B.V. All rights reserved. Y1 - 2008 UR - http://www.sciencedirect.com/science/article/pii/S0022231307003262 U6 - https://doi.org/10.1016/j.jlumin.2007.10.018 ER - TY - JOUR A1 - Tiseanu, Carmen A1 - Geßner, Andre A1 - Kumke, Michael Uwe A1 - Parvulescu, V. T1 - Dehydration and rehydration effects on the photoluminescence properties of terbium-exchanged MFI type materials Y1 - 2008 U6 - https://doi.org/10.1016/j.jnoncrysol.2007.11.017 ER -