Harry Donker - Academia.edu (original) (raw)

Papers by Harry Donker

Research paper thumbnail of Spin-allowed and spin-forbidden fd emission from Er3+ and LiYF4

Physical Review B, 1998

ABSTRACT

Research paper thumbnail of Vacuum-ultraviolet spectroscopy and quantum cutting for Gd3+ in LiYF4

Physical Review B, 1997

... Two-photon absorption spectroscopy has been used successfully to overcome this problem,10 but... more ... Two-photon absorption spectroscopy has been used successfully to overcome this problem,10 but to date this ... been found in several host lattices.15 These emissions are all in the ultraviolet region ... the basis of the energy-level scheme of Gd3 one can expect a visible emission in ...

Research paper thumbnail of Formation and decay of charge carriers in hybrid MDMO-PPV:ZnO bulk heterojunctions produced from a ZnO precursor

Superlattices and Microstructures, 2005

Recently, there has been growing interest in photovoltaic cells based on bulk heterojunctions of ... more Recently, there has been growing interest in photovoltaic cells based on bulk heterojunctions of ZnO and a conjugated polymer. In this work, the photophysical processes in a hybrid film of ZnO with MDMO-PPV were studied by means of optical absorption spectroscopy and microwave photoconductivity measurements. Films were prepared from a blend of a ZnO precursor and MDMO-PPV in which the

Research paper thumbnail of Spectroscopy and Photophysics of Self-Organized Zinc Porphyrin Nanolayers. 1. Optical Spectroscopy of Excitonic Interactions Involving the Soret Band

The Journal of Physical Chemistry B, 2005

The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in... more The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in 5-25-nmthick films spin-coated onto quartz slides have been investigated by optical spectroscopy. Analysis of the polarized absorption spectra using a dipole-dipole exciton model with two mutually perpendicular transition dipole moments per molecule shows that the films are built from linear aggregates, i.e., stacks with a slippeddeck-of-cards configuration. The molecular planes of the porphyrins in the stacks are found to be perpendicularly oriented with respect to the substrate plane. Assuming a value of 2-3 for the dielectric constant of the film, from the excitonic shift, an angle of 44°( 3°and an interplanar distance of 0.35-0.36 nm between adjacent porphyrins are calculated, close to the ground-state geometry in solution. The ordering in these films was further investigated by the effects of various solvents and temperature annealing. Spin-coating from toluene as a solvent results in highly ordered films, and annealing of these films has little effect on their absorption spectra. However, spin-coating from chloroform or pyridine or exposure of the films to these solvents in their vapor phases changes their ordering presumably due to incorporation of residual solvent molecules. Annealing yields absorption spectra identical to those of films spin-coated from toluene. The absorption spectra are insensitive to atmospheric moisture, in contrast to those of zinc tetraphenylporphyrin films lacking octyl substituents.

Research paper thumbnail of Nonisotropic Excitation Energy Transport in Organized Molecular Systems:  Monte Carlo Simulation-Based Analysis of Fluorescence and Fluorescence Anisotropy Decay

The Journal of Physical Chemistry A, 2001

An improved application is presented of the Monte Carlo method including simultaneous parameter f... more An improved application is presented of the Monte Carlo method including simultaneous parameter fitting to analyze the experimental time-resolved fluorescence and fluorescence anisotropy decay of two organized molecular systems exhibiting a number of different, nonisotropic energy transfer processes. Using physical models and parameter fitting for these systems, the Monte Carlo simulations yield a final set of parameters, which characterize the energy transfer processes in the investigated systems. The advantages of such a simulation-based analysis for global parametric fitting are discussed. Using this approach energy transfer processes have been analyzed for two porphyrin model systems, i.e., spin-coated films of zinc tetra-(octylphenyl)-porphyrins (ZnTOPP) and the tetramer of zinc mono(4-pyridyl)triphenylporphyrin (ZnM(4-Py)TrPP). For the ZnTOPP film energy transfer rate constants of ∼1 × 10 12 s -1 and ∼80 × 10 9 s -1 have been found, and are assigned to intra-and interstack transfer, respectively. For the tetramers, the transfer rate constants of 38 × 10 9 and 5 × 10 9 s -1 correspond to energy transfer to nearest and next nearest neighbor molecules, respectively. The results are in agreement with a Förster type energy transfer mechanism. 9499 P I | ∼ 3/2 (1sin 2 R sin 2 φ) (cos φ cos R cos sin ηsin φ sin sin η + cos φ sin R cos η) 2 (11) P I ⊥ ∼ 3 / 2 (1sin 2 R sin 2 φ) (-sin R cos sin η + cos R cos η) 2 (12) Energy Transport in Organized Molecular Systems

Research paper thumbnail of Spectroscopic Properties of a Self-Assembled Zinc Porphyrin Tetramer II. Time-Resolved Fluorescence Spectroscopy

The Journal of Physical Chemistry A, 2001

... The Netherlands. Bas Gobets, Ivo van Stokkum, and Rienk van Grondelle. Faculty of Sciences, D... more ... The Netherlands. Bas Gobets, Ivo van Stokkum, and Rienk van Grondelle. Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. J. Phys. Chem. A ...

Research paper thumbnail of UV Polymerization of Oligothiophenes and Their Application in Nanostructured Heterojunction Solar Cells

Macromolecules, 2004

... 1,49 To lower the resistance of the cells, a film of PEDOT:PSS (poly(3,4-ethylenedioxythiophe... more ... 1,49 To lower the resistance of the cells, a film of PEDOT:PSS (poly(3,4-ethylenedioxythiophene: poly(styrenesulfonate) (Bayer AG, Baytron P) is spin-coated on top of the TiO 2 /oligothiophenes blend. PEDOT-PSS is a highly doped p-type material, selectively conducting holes. ...

Research paper thumbnail of Luminescence of the Te4+ ion in ZrP2O7

Journal of Solid State Chemistry, 1989

ABSTRACT The luminescence spectra and decay times of the Te4+ ion in ZrP2O7 are reported and disc... more ABSTRACT The luminescence spectra and decay times of the Te4+ ion in ZrP2O7 are reported and discussed. ZrP2O7:Te4+ shows a blue emission band with a maximum at 21,200 cm-1 at LHeT. Decay time measurements reveal the presence of at least two kinds of Te4+ ions. This is not apparent from the luminescence spectra, indicating that the Te4+ ions have quite similar environments. The 1S0 --> 3P1 excitation band of the Te4+ ion is situated at 38,250 cm-1. A comparison is made with the luminescence of related systems.

Research paper thumbnail of Photon cascade emission in SrAlF 5 :Pr 3 

Journal of Physics: Condensed Matter, 2002

The optical properties of SrAlF 5 :Pr 3+ are studied. Emission measurements up to 1200 nm under b... more The optical properties of SrAlF 5 :Pr 3+ are studied. Emission measurements up to 1200 nm under blue-light excitation in the 3 P 2 level reveal a large number of emissions all originating from the 3 P 0 level and the 1 D 2 level. Under vacuum ultraviolet excitation in the 4f 1 5d 1 bands, emission from the 1 S 0 level, followed by emission from the 3 P 0 level and the 1 D 2 level takes place. This is known as the photon cascade emission process. The excitation spectrum of the 1 S 0 emission was measured and was compared with the excitation spectrum of SrAlF 5 :Ce 3+ . The spectrum for SrAlF 5 :Pr 3+ compared to SrAlF 5 :Ce 3+ is at about 12 240 cm −1 higher energy. A study of the x-ray-excited emission in the temperature region from 100 to 350 K was performed, determining the processes responsible for both 1 S 0 and 3 P 0 / 1 D 2 emissions.

Research paper thumbnail of Quantum cutting through downconversion in rare-earth compounds

Journal of Luminescence, 2000

A new concept for the conversion of vacuum ultraviolet radiation to visible light is described wh... more A new concept for the conversion of vacuum ultraviolet radiation to visible light is described which makes it posible to obtain two visible photons for each vacuum ultraviolet photon absorbed (quantum cutting). The feasibilty of this concept, called downconversion, is demonstrated by two examples: LiGdF : Eu> and LiGdF : Er>, Tb>. The highest e$ciencies are achieved for LiGdF : Eu>. Upon excitation of Gd> with a high-energy photon, two visible photons can be emitted through an e$cient two-step energy transfer process, with a quantum e$ciency that approaches 200%.

Research paper thumbnail of Visible quantum cutting in Eu3+-doped gadolinium fluorides via downconversion

Journal of Luminescence, 1999

Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum... more Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum cutting) is reported for LiGdF : Eu> and GdF : Eu>. For every Gd> ion excited in the G ( levels (around 50 000 cm\) or higher, two visible photons can be emitted due to D ( PF ( transitions on two Eu> ions. The "rst Eu> ion is excited into the D level by cross relaxation of the energy corresponding to the G ( PP ( transition on Gd>. The second Eu> ion is excited by direct energy transfer of the remaining energy from Gd> (P ( ) to Eu>. It is shown that this two-step energy transfer process is very e$cient at room temperature. Since this process is the opposite of the well-known upconversion process, we call it downconversion.

Research paper thumbnail of Downconversion: a new route to visible quantum cutting

Journal of Alloys and Compounds, 2000

To obtain vacuum ultraviolet (VUV) phosphors with quantum efficiencies higher than 100%, the conc... more To obtain vacuum ultraviolet (VUV) phosphors with quantum efficiencies higher than 100%, the concept of downconversion is used. In a downconversion process a VUV photon is split into two visible photons by making use of energy transfer between different rare earth 31 31 31 31 31 ions. Two examples of downconversion couples are discussed, viz. the Gd -Eu couple and the Er -Gd -Tb system. X-ray powder diffraction. LiGdF has the inverse scheelite 4 0925-8388 / 00 / $ -see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 99 )00755-0 5 7 1(c) illustrates the possibility of cross relaxation between a D → F transition. J J quantum cutting ion. It can be calculated that several J 5 10 31 4 energy migration step, however, all D levels can become transitions from the 4f 5d state of Er to different F J J 4 3 1 populated by multiphonon relaxation from higher levels. and G states overlap Gd transitions from the ground J 5 6 6 6

Research paper thumbnail of A study of energy transfer processes in zinc–porphyrin films using Monte Carlo simulation of fluorescence decay

Chemical Physics Letters, 2001

Energy transfer in thin ®lms of zinc tetra(-octylphenyl)-porphyrin (ZnTOPP) doped with the copper... more Energy transfer in thin ®lms of zinc tetra(-octylphenyl)-porphyrin (ZnTOPP) doped with the copper (CuTOPP) or freebase H 2 TOPP analogues were investigated by time-resolved¯uorescence and Monte Carlo simulations, applied to a single domain model of parallel porphyrin stacks. Rate constants for intra-and inter-stack energy transfer are 0:8±1:1 Â 10 12 and 71±91 Â 10 9 s À1 , respectively. The¯uorescence lifetimes for ZnTOPP and H 2 TOPP ®lms are 1:80±1:88 Â 10 À9 and 6:8±7:3 Â 10 À9 s. The rate constant for H 2 TOPP to ZnTOPP back transfer is 8:8±9:4 Â 10 6 s À1 . The results agree with those of a previous analytical analysis . Ó

Research paper thumbnail of Jahn-Teller distortion in the excited state of tellurium(IV) in Cs2MCl6 (M=Zr, Sn)

Chemical Physics Letters, 1988

The luminescence spectra of the diluted systems CszZrClb: Te4+ and Cs#Q,: Te4+ are reported at li... more The luminescence spectra of the diluted systems CszZrClb: Te4+ and Cs#Q,: Te4+ are reported at liquid-helium and room temperature. The shape of the excitation spectrum of the Te 4+ luminescence reveals a dynamic Jahn-Teller distortion in the excited state. At low temperatures the Te4+ emission shows a vibrational progression in the e8 mode. The same vibrational mode is derived from the temperature dependence of the splitting of the A excitation band. Vibrational structure is also observed in the B band of the excitation spectrum of Cs#nCl,: Te4+.

Research paper thumbnail of 7-Dimethylamino-1-methyl-quinolinium Tetrafluoroborate; A Remarkably Stable Fluorescent Probe for Polymer Characterizations

Polymeric Materials Science and Engineering, 2004

Fluorescent probes and labels are useful tools to probe a medium. Fluorescent probe technology is... more Fluorescent probes and labels are useful tools to probe a medium. Fluorescent probe technology is a very versatile technique, which requires probe molecules to be incorporated in a medium, excitation light to reach the probes and emission light to be harvested. Structure development in a sample can be investigated as a function of time and position. In our research mobility sensitive probes are developed for application in polymers and polymerizing systems. The probes develop a large dipole moment in the excited state and ...

Research paper thumbnail of Liquid Crystalline Perylene Diimides:  Architecture and Charge Carrier Mobilities

Journal of the American Chemical Society, 2000

The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by diffe... more The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by differential scanning calorimetry and polarized optical microscopy. The occurrence of multiple phase transitions indicates several crystalline and several liquid crystalline phases. X-ray ...

Research paper thumbnail of Spin-allowed and spin-forbidden fd emission from Er3+ and LiYF4

Physical Review B, 1998

ABSTRACT

Research paper thumbnail of Vacuum-ultraviolet spectroscopy and quantum cutting for Gd3+ in LiYF4

Physical Review B, 1997

... Two-photon absorption spectroscopy has been used successfully to overcome this problem,10 but... more ... Two-photon absorption spectroscopy has been used successfully to overcome this problem,10 but to date this ... been found in several host lattices.15 These emissions are all in the ultraviolet region ... the basis of the energy-level scheme of Gd3 one can expect a visible emission in ...

Research paper thumbnail of Formation and decay of charge carriers in hybrid MDMO-PPV:ZnO bulk heterojunctions produced from a ZnO precursor

Superlattices and Microstructures, 2005

Recently, there has been growing interest in photovoltaic cells based on bulk heterojunctions of ... more Recently, there has been growing interest in photovoltaic cells based on bulk heterojunctions of ZnO and a conjugated polymer. In this work, the photophysical processes in a hybrid film of ZnO with MDMO-PPV were studied by means of optical absorption spectroscopy and microwave photoconductivity measurements. Films were prepared from a blend of a ZnO precursor and MDMO-PPV in which the

Research paper thumbnail of Spectroscopy and Photophysics of Self-Organized Zinc Porphyrin Nanolayers. 1. Optical Spectroscopy of Excitonic Interactions Involving the Soret Band

The Journal of Physical Chemistry B, 2005

The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in... more The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in 5-25-nmthick films spin-coated onto quartz slides have been investigated by optical spectroscopy. Analysis of the polarized absorption spectra using a dipole-dipole exciton model with two mutually perpendicular transition dipole moments per molecule shows that the films are built from linear aggregates, i.e., stacks with a slippeddeck-of-cards configuration. The molecular planes of the porphyrins in the stacks are found to be perpendicularly oriented with respect to the substrate plane. Assuming a value of 2-3 for the dielectric constant of the film, from the excitonic shift, an angle of 44°( 3°and an interplanar distance of 0.35-0.36 nm between adjacent porphyrins are calculated, close to the ground-state geometry in solution. The ordering in these films was further investigated by the effects of various solvents and temperature annealing. Spin-coating from toluene as a solvent results in highly ordered films, and annealing of these films has little effect on their absorption spectra. However, spin-coating from chloroform or pyridine or exposure of the films to these solvents in their vapor phases changes their ordering presumably due to incorporation of residual solvent molecules. Annealing yields absorption spectra identical to those of films spin-coated from toluene. The absorption spectra are insensitive to atmospheric moisture, in contrast to those of zinc tetraphenylporphyrin films lacking octyl substituents.

Research paper thumbnail of Nonisotropic Excitation Energy Transport in Organized Molecular Systems:  Monte Carlo Simulation-Based Analysis of Fluorescence and Fluorescence Anisotropy Decay

The Journal of Physical Chemistry A, 2001

An improved application is presented of the Monte Carlo method including simultaneous parameter f... more An improved application is presented of the Monte Carlo method including simultaneous parameter fitting to analyze the experimental time-resolved fluorescence and fluorescence anisotropy decay of two organized molecular systems exhibiting a number of different, nonisotropic energy transfer processes. Using physical models and parameter fitting for these systems, the Monte Carlo simulations yield a final set of parameters, which characterize the energy transfer processes in the investigated systems. The advantages of such a simulation-based analysis for global parametric fitting are discussed. Using this approach energy transfer processes have been analyzed for two porphyrin model systems, i.e., spin-coated films of zinc tetra-(octylphenyl)-porphyrins (ZnTOPP) and the tetramer of zinc mono(4-pyridyl)triphenylporphyrin (ZnM(4-Py)TrPP). For the ZnTOPP film energy transfer rate constants of ∼1 × 10 12 s -1 and ∼80 × 10 9 s -1 have been found, and are assigned to intra-and interstack transfer, respectively. For the tetramers, the transfer rate constants of 38 × 10 9 and 5 × 10 9 s -1 correspond to energy transfer to nearest and next nearest neighbor molecules, respectively. The results are in agreement with a Förster type energy transfer mechanism. 9499 P I | ∼ 3/2 (1sin 2 R sin 2 φ) (cos φ cos R cos sin ηsin φ sin sin η + cos φ sin R cos η) 2 (11) P I ⊥ ∼ 3 / 2 (1sin 2 R sin 2 φ) (-sin R cos sin η + cos R cos η) 2 (12) Energy Transport in Organized Molecular Systems

Research paper thumbnail of Spectroscopic Properties of a Self-Assembled Zinc Porphyrin Tetramer II. Time-Resolved Fluorescence Spectroscopy

The Journal of Physical Chemistry A, 2001

... The Netherlands. Bas Gobets, Ivo van Stokkum, and Rienk van Grondelle. Faculty of Sciences, D... more ... The Netherlands. Bas Gobets, Ivo van Stokkum, and Rienk van Grondelle. Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. J. Phys. Chem. A ...

Research paper thumbnail of UV Polymerization of Oligothiophenes and Their Application in Nanostructured Heterojunction Solar Cells

Macromolecules, 2004

... 1,49 To lower the resistance of the cells, a film of PEDOT:PSS (poly(3,4-ethylenedioxythiophe... more ... 1,49 To lower the resistance of the cells, a film of PEDOT:PSS (poly(3,4-ethylenedioxythiophene: poly(styrenesulfonate) (Bayer AG, Baytron P) is spin-coated on top of the TiO 2 /oligothiophenes blend. PEDOT-PSS is a highly doped p-type material, selectively conducting holes. ...

Research paper thumbnail of Luminescence of the Te4+ ion in ZrP2O7

Journal of Solid State Chemistry, 1989

ABSTRACT The luminescence spectra and decay times of the Te4+ ion in ZrP2O7 are reported and disc... more ABSTRACT The luminescence spectra and decay times of the Te4+ ion in ZrP2O7 are reported and discussed. ZrP2O7:Te4+ shows a blue emission band with a maximum at 21,200 cm-1 at LHeT. Decay time measurements reveal the presence of at least two kinds of Te4+ ions. This is not apparent from the luminescence spectra, indicating that the Te4+ ions have quite similar environments. The 1S0 --> 3P1 excitation band of the Te4+ ion is situated at 38,250 cm-1. A comparison is made with the luminescence of related systems.

Research paper thumbnail of Photon cascade emission in SrAlF 5 :Pr 3 

Journal of Physics: Condensed Matter, 2002

The optical properties of SrAlF 5 :Pr 3+ are studied. Emission measurements up to 1200 nm under b... more The optical properties of SrAlF 5 :Pr 3+ are studied. Emission measurements up to 1200 nm under blue-light excitation in the 3 P 2 level reveal a large number of emissions all originating from the 3 P 0 level and the 1 D 2 level. Under vacuum ultraviolet excitation in the 4f 1 5d 1 bands, emission from the 1 S 0 level, followed by emission from the 3 P 0 level and the 1 D 2 level takes place. This is known as the photon cascade emission process. The excitation spectrum of the 1 S 0 emission was measured and was compared with the excitation spectrum of SrAlF 5 :Ce 3+ . The spectrum for SrAlF 5 :Pr 3+ compared to SrAlF 5 :Ce 3+ is at about 12 240 cm −1 higher energy. A study of the x-ray-excited emission in the temperature region from 100 to 350 K was performed, determining the processes responsible for both 1 S 0 and 3 P 0 / 1 D 2 emissions.

Research paper thumbnail of Quantum cutting through downconversion in rare-earth compounds

Journal of Luminescence, 2000

A new concept for the conversion of vacuum ultraviolet radiation to visible light is described wh... more A new concept for the conversion of vacuum ultraviolet radiation to visible light is described which makes it posible to obtain two visible photons for each vacuum ultraviolet photon absorbed (quantum cutting). The feasibilty of this concept, called downconversion, is demonstrated by two examples: LiGdF : Eu> and LiGdF : Er>, Tb>. The highest e$ciencies are achieved for LiGdF : Eu>. Upon excitation of Gd> with a high-energy photon, two visible photons can be emitted through an e$cient two-step energy transfer process, with a quantum e$ciency that approaches 200%.

Research paper thumbnail of Visible quantum cutting in Eu3+-doped gadolinium fluorides via downconversion

Journal of Luminescence, 1999

Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum... more Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum cutting) is reported for LiGdF : Eu> and GdF : Eu>. For every Gd> ion excited in the G ( levels (around 50 000 cm\) or higher, two visible photons can be emitted due to D ( PF ( transitions on two Eu> ions. The "rst Eu> ion is excited into the D level by cross relaxation of the energy corresponding to the G ( PP ( transition on Gd>. The second Eu> ion is excited by direct energy transfer of the remaining energy from Gd> (P ( ) to Eu>. It is shown that this two-step energy transfer process is very e$cient at room temperature. Since this process is the opposite of the well-known upconversion process, we call it downconversion.

Research paper thumbnail of Downconversion: a new route to visible quantum cutting

Journal of Alloys and Compounds, 2000

To obtain vacuum ultraviolet (VUV) phosphors with quantum efficiencies higher than 100%, the conc... more To obtain vacuum ultraviolet (VUV) phosphors with quantum efficiencies higher than 100%, the concept of downconversion is used. In a downconversion process a VUV photon is split into two visible photons by making use of energy transfer between different rare earth 31 31 31 31 31 ions. Two examples of downconversion couples are discussed, viz. the Gd -Eu couple and the Er -Gd -Tb system. X-ray powder diffraction. LiGdF has the inverse scheelite 4 0925-8388 / 00 / $ -see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 99 )00755-0 5 7 1(c) illustrates the possibility of cross relaxation between a D → F transition. J J quantum cutting ion. It can be calculated that several J 5 10 31 4 energy migration step, however, all D levels can become transitions from the 4f 5d state of Er to different F J J 4 3 1 populated by multiphonon relaxation from higher levels. and G states overlap Gd transitions from the ground J 5 6 6 6

Research paper thumbnail of A study of energy transfer processes in zinc–porphyrin films using Monte Carlo simulation of fluorescence decay

Chemical Physics Letters, 2001

Energy transfer in thin ®lms of zinc tetra(-octylphenyl)-porphyrin (ZnTOPP) doped with the copper... more Energy transfer in thin ®lms of zinc tetra(-octylphenyl)-porphyrin (ZnTOPP) doped with the copper (CuTOPP) or freebase H 2 TOPP analogues were investigated by time-resolved¯uorescence and Monte Carlo simulations, applied to a single domain model of parallel porphyrin stacks. Rate constants for intra-and inter-stack energy transfer are 0:8±1:1 Â 10 12 and 71±91 Â 10 9 s À1 , respectively. The¯uorescence lifetimes for ZnTOPP and H 2 TOPP ®lms are 1:80±1:88 Â 10 À9 and 6:8±7:3 Â 10 À9 s. The rate constant for H 2 TOPP to ZnTOPP back transfer is 8:8±9:4 Â 10 6 s À1 . The results agree with those of a previous analytical analysis . Ó

Research paper thumbnail of Jahn-Teller distortion in the excited state of tellurium(IV) in Cs2MCl6 (M=Zr, Sn)

Chemical Physics Letters, 1988

The luminescence spectra of the diluted systems CszZrClb: Te4+ and Cs#Q,: Te4+ are reported at li... more The luminescence spectra of the diluted systems CszZrClb: Te4+ and Cs#Q,: Te4+ are reported at liquid-helium and room temperature. The shape of the excitation spectrum of the Te 4+ luminescence reveals a dynamic Jahn-Teller distortion in the excited state. At low temperatures the Te4+ emission shows a vibrational progression in the e8 mode. The same vibrational mode is derived from the temperature dependence of the splitting of the A excitation band. Vibrational structure is also observed in the B band of the excitation spectrum of Cs#nCl,: Te4+.

Research paper thumbnail of 7-Dimethylamino-1-methyl-quinolinium Tetrafluoroborate; A Remarkably Stable Fluorescent Probe for Polymer Characterizations

Polymeric Materials Science and Engineering, 2004

Fluorescent probes and labels are useful tools to probe a medium. Fluorescent probe technology is... more Fluorescent probes and labels are useful tools to probe a medium. Fluorescent probe technology is a very versatile technique, which requires probe molecules to be incorporated in a medium, excitation light to reach the probes and emission light to be harvested. Structure development in a sample can be investigated as a function of time and position. In our research mobility sensitive probes are developed for application in polymers and polymerizing systems. The probes develop a large dipole moment in the excited state and ...

Research paper thumbnail of Liquid Crystalline Perylene Diimides:  Architecture and Charge Carrier Mobilities

Journal of the American Chemical Society, 2000

The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by diffe... more The phase behavior of three N-alkyl-substituted perylene diimide derivatives is examined by differential scanning calorimetry and polarized optical microscopy. The occurrence of multiple phase transitions indicates several crystalline and several liquid crystalline phases. X-ray ...