H. Gratz

Photo-physical characterization of rhodamine 6G in a 2-hydroxyethyl-methacrylate methyl-methacrylate copolymer

Abstract Some photo-physical parameters of 1×10−4 and 5.9×10−4 M samples of rhodamine 6G in a 2-hydroxyethyl-methacrylate methyl-methacrylate copolymer (volume mixture 1:1) are determined and compared with rhodamine 6G in methanol. They include the absorption cross-section and stimulated emission cross-section spectra, the fluorescence quantum distributions, quantum yields and lifetimes. The photo-degradation under steady-state and pulsed excitation is investigated. The saturable absorption behaviour under picosecond laser excitation is studied.

Photophysical characterization of pyrromethene dyes in solid matrices of acrylic copolymers

Abstract Some photophysical parameters of the pyrromethene laser dye PM567 and of two newly synthesized pyrromethene laser dyes, P5Ac and P10Ac, in solid matrices of different acrylic copolymers and in corresponding mimetic liquid solutions are determined. They include absorption cross-section and stimulated emission cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes. The saturable absorption behaviour due to picosecond laser pulse excitation is studied. The photodegradation under cw laser excitation and under pulsed picosecond pulse excitation is investigated.

Singlet-singlet excited-state absorption and triplet-triplet absorption of meso-tetraphenylporphine

Abstract The singlet–singlet excited-state absorption cross-section spectrum and the triplet–triplet absorption cross-section spectrum of meso-tetraphenylporphine (H2TPP) are determined in the wavelength range from 390 to 1450 nm. The S1-singlet state is populated by intense picosecond pump pulse absorption (wavelength 527 nm, duration 6 ps). The T1-triplet state is populated by S1–T1 intersystem crossing. The singlet–singlet absorption and the triplet–triplet absorption are probed with picosecond spectral light continua passing the sample after appropriate time delays. Absolute singlet–singlet and triplet–triplet absorption cross-sections are obtained by numerical simulation of the absorption dynamics. The similarity of the S1-band-and T1-band-based excited-state absorption cross-section spectra indicate a strong higher excited-state spin–orbit coupling.

Nanometer particle size, pore size, and specific surface determination of colloidal suspensions and porous glasses by Rayleigh light scattering

Abstract Rayleigh scattering of a HeNe laser is applied to determine the particle size of colloidal silicon dioxide suspensions (Ludox CL-X and Ludox PG), and the effective sphere diameter of Vycor glass, and of silicate sol—gel glasses. The pore sizes and specific surfaces of the samples are estimated.

Saturable absorption dynamics in the triplet system and triplet excitation induced singlet fluorescence of some organic molecules

Abstract The triplet saturable absorption behaviour of the xanthene dyes eosin Y, erythrosin B, and rose bengal and of the fullerene molecule C 70 is studied. The molecules are excited to the S 1 -state by intense picosecond pulses (wavelength λ P =527 nm). They relax dominantly to the triplet system by intersystem crossing. The triplet–triplet saturable absorption is investigated with time-delayed intense picosecond pulses (wavelength λ L =1054 nm) in the transparency region of the molecules in the singlet ground state. Higher excited-state triplet absorption cross-sections and higher excited-state triplet relaxation times are determined by numerical simulation of the experimental results. Time-resolved fluorescence measurements reveal higher excited-state triplet to singlet back-intersystem-crossing and multi-step triplet photoionization. Additionally the two-photon absorption cross-sections at λ L =1054 nm are determined by measurement of the fundamental pulse two-photon induced fluorescence relative to the second-harmonic pulse single-photon induced fluorescence.

Intersystem-crossing and excited-state absorption of C70 studied by picosecond pump and probe absorption and fluorescence measurements

Abstract The singlet and triplet absorption and emission dynamics of C 70 in toluene is studied with a picosecond Nd:glass laser double-pulse pump and probe transmission and fluorescence measurement technique. The singlet S 1 excited-state absorption ( σ ex,L ≈ 6 × 10 −17 cm 2 ), the triplet T 1 absorption ( σ T ≈ 4.2 × 10 −17 cm 2 ), and the triplet T 2 absorption ( σ ex,T ≈ 6 × 10 −17 cm 2 ) at 527 nm are determined. The singlet to triplet intersystem-crossing is studied by double pump pulse induced fluorescence signal analysis and by double probe pulse transmission measurements. The yield of triplet formation is found to be near to unity.

Dye sorption studies and specific surface determination of porous silicate sol-gel glasses

Abstract The adsorption and desorption of rhodamine 6G and oxazine 750 molecules in methanol to and from porous silicate sol—gel monoliths and pulverised samples is studied over a wide concentration region. Chemisorption and physisorption are observed. The adsorption data are fitted to a combined Langmuir and Brunauer—Emmett—Teller (BET) equation. Effective adsorbate occupation areas are obtained by investigating transparent porous Gelsil glasses of known specific surface. They are related to the dye solubility. The sorption and desorption isotherm of a self-prepared silicate xerogel is measured. Its specific surface and average pore diameter is determined.