Rubrene nanocystal is a red colored polycyclic aromatic hydrocarbon. It exhibit prompt fluorescence lifetime of 16±lns, close to the natural lifetime and B-type of delayed fluorescence of 48±5 ns. Rubrene excited states can act as quenchers for the fluorescence. Increasing the laser power leads to a saturation of fluorescence and a reduction of its lifetime. Raman Stokes shift was observed at 670 nm in the fluorescence spectrum. The fluorescence emission spectrum of rubrene molecule in solution mirrors the shape of the absorption spectrum regardless of the excitation frequency.
Flash spectroscopic study of p-methoxy-styrene (hereafter PMS) in water at room temperature gave first order photochemical reactions. In the first step an excited singlet S1 is created then S1›S0 transitions were recorded. The 1/e decay time of promt fluorescence of PMS in water at room temperature were measured by using flash photolysis technique, and the fluorescence decay time was found to be 19 ns. Due to the various quenching processes neither delayed fluorescences nor triplet-triplet emissions could be recorded.
High resolution, S0-› Sn and S n-› S0 electronic absorption and prompt fluorescence of 1,2,5,6-dibenzanthracene in polymethylmethacrylate were experimentally observed by flash and laser flash photolysis technique. In the first step, an excited singlet state is created by nanosecond optical pumping system, then electronically excited molecule returns to the ground state by emitting high resolution prompt fluorescence at the room temperature. The decay time of S 1 state was measured by laser flash photolysis system, and found to be 12±1 nsec.
Extinction coefficients, B-type delayed fluorescence and some photophysical properties of coronene in solution are studied by photolysis, flash photolysis, and laser flash photolysis techniques. For B-type delayed flourescence coronene molecules were excited in a two-step process. In the first step, an excited singlet S1 was created, which undergoes intersystem crossing to T1 state; then T-T absorption creates an excited triplet of coronene molecule, which returns to the first excited singlet level S1 by intersystem crossing from T2 to S1. The recreated first excited singlet state of coronene decays back to the ground state So by em . . .itting B-type delayed flourescence
Salicylindeneaniline originally crystallized from a solution has lemon yellow colour. Irradiation with near ultraviolet causes the colour change from yellow to red. The red state changes spontaneously back to yellow. This change is accelerated by visible light. Kinetic data are reported in the temperature range between 18.5 and 55°C, for the dark fading reactions of the coloured isomers formed by the ultraviolet irradiation. First order reactions were observed, activation energies and entropies of activation are reported. The observation of T-T absorption was complicated due to coloured isomer formation during the optical pumping.
The observation of triplet-triplet absorption of salicylidene-p-anicidine is complicated because of the possible colored isomer formation during the optical pumping, between the S0 › Sn and T 1 › Tn absorptions. The short-lived (singlet-singlet) and long-lived (triplet-triplet) absorption spectra were recorded photographically by microsecond flash photolysis and nanosecond laser flash photolysis techniques. Salicylidene complexes were purified by repeated recrystallisation until further recrystallisation produced no further changes for x- ray diffraction pattern and optical absorption and emission properties.
Formation and decay of the phenoxyl radical in the vapor phase were studied by flash photolysis technique at room temperature and subsequent reactions have been investigated by kinetic spectroscopy and gas liquid chromotography. The extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95 × 104 Mol-1.1.cm-1.
The ultraviolet high photon flux light induced high resolution optical discrete absorption and superfluorescence discrete spectra of spectrosil quartz were recorded photographically first time in the ultraviolet region at room temperature. This novel discrete transitions observed experimentally between two electronic energy level system by depopulating the ground state of spectrosil quartz in the solid state phase. The integrated areas of the absorption and emission bands were identical and recorded at the highest-quality images at room temperature. This two-level emission system showed that this pure undoped fiber material is not s . . .uitable for optical fiber communications in the ultraviolet region only. It is suitable for the visible region. But it will be a perfect device for optoelectronics, optical spectroscopy, photonics laboratory experiments for transmission lines, power electronics and laser research
Silicon atomic fluorescence was excited within a carbon atomiser by high voltage (12 kV) discharge technique. Silicon atoms in different rock samples were excited to the upper electronic energy levels, then excited silicon atoms returned to the ground state by emitting characteristic fluorescence lines. All fluorescence transitions observed were resonance lines. Fluorescence lines of silicon were observed at 250.69, 251.43, 251.61, 252.41 and 252.81 nm, as intense discrete emission lines. These emission lines were calibrated by iron arc and mercury arc emission spectra.
The observation of triplet-triplet absorption of salicylidene-p-bromo aniline, is complicated by the possible colored isomer formation during the optical pumping. The short-lived (singlet-singlet) and long-lived (triplet-triplet) absorption spectra were recorded photographically by microsecond flash and nanosecond laser flash photolysis techniques. Salicylidene aniline complexes were purified by repeated recrystallisation until further recrystallisation produced no further changes for x-ray diffraction pattern and optical absorption, emission properties.