I. Pócsik

Origin of the D peak in the Raman spectrum of microcrystalline graphite

Abstract We have studied the D peak in the Raman spectrum of polycrystalline graphite as a function of excitation energy in the range from 1.16 to 4.3 eV. The D peak disperses with excitation energy (≈50 cm−1/eV) and its intensity decreases with increasing laser energy. The dispersion of the D peak is explained in terms of a novel k → -selective resonant Raman scattering process. The scattering cross-section is resonantly enhanced for phonons on one branch in the phonon dispersion curves which have the same k → -vector as the electronic transition responsible for the resonance.

The state of water in normal and senile cataractous lenses studied by nuclear magnetic resonance

Normal and senile cataractous lenses were studied by nuclear magnetic resonance in order to get information about the state of water during the progression of cataract. Water proton spin-spin (T2) and spin-lattice relaxation times—in the laboratory and the rotating frame—() were measured at 34 and 90 MHz. At temperatures below −9°C the relaxation times of protons in “non-freezable” component of lens water were measured as a function of the temperature, and T1 and T2 relaxation times were found to be the same for both the normal and the cataractous lenses. At temperatures above −9°C a marked difference in relaxation times T1 and T2 was found between normal and completely opaque lenses. It was concluded that the most characteristic difference between the normal and completely opaque lenses should be accounted for by the change in the “bound”-to-“free” ratio of lens water.

The state of water in normal human, bird and fish eye lenses

Abstract The state of water was studied in normal human, fish and bird eye lenses. Free induction decay as well as nuclear spin-lattice and nuclear spin-spin relaxation time measurements were carried out by NMR method. The amount of non-freezable water per unit protein quantity was determined and the activation energy of the motion of the water molecules responsible for the relaxation was estimated. These results were compared with the ideas of Kuch and Yu concerning difference in protein conformation of the lens crystallins.

The role of hydrogen in luminescence of electrochemically oxidized porous Si layer

Abstract Remarkable improvements of photoluminescence (PL) efficiency together with large blueshift of PL peak wavelength have been achieved by electrochemical oxidation. It is known from Fourier transform infrared (FT-IR) measurements that the SiO 2 covering on pore walls has discontinuities where the surface states are terminated by hydrogen. Dramatic degradation of luminescence transitions in anodically oxidized PSL, due to thermal hydrogen desorption, indicates the importance of hydrogen in electrochemical surface passivation.

Water fractions in normal and senile cataractous eye lenses studied by NMR

The state of water and water fractions in normal and senile cataractous eye lenses was studied by the NMR method. Combining NMR with vacuum dehydration provided additional information on multifractional samples. A new mathematical procedure is presented which separates the characteristic parameters of the different fractions and helps to determine the relaxation times and amounts of the fractions. The measurement accuracy enables separation of three different water fractions both in normal and in cataractous lenses.

Polarization memory of photoluminescence in a-C:H film

Abstract Large polarization memory effects of photoluminescence were observed in a-C:H films, its degree decreased from 40 % on the high energy side to zero on the low energy side of the luminescence band. Radiative recombination of strongly localized electron-hole pairs is suggested as being the mechanism responsible for the polarization memory of luminescence.

Luminescence efficiency enhancement in laser soaked hydrogenated amorphous carbon films

An unexpected effect of laser soaking was observed on the properties of annealed a‐C:H films. The photoluminescence (PL) intensity was increased up to six times and, the spectrum was blue shifted in samples exposed to an unfocused Ar+ laser beam. The time dependence of the PL intensity increase was found to be exponential up to saturation with characteristic times around 103 s. The observed changes were influenced by illumination intensity and sample properties. These results are corroborated by a PL mechanism when excitation and recombination take place on π‐bonded clusters.

C.P.-D.D.-M.A.S. 13C-N.M.R. investigations of anhydrous and hydrated cyclomalto-oligosaccharides: The role of water of hydration

Abstract Hydrated and anhydrous cyclomaltohexaose, cyclomaltoheptaose, and cyclomalto-octaose (cyclodextrins) have been investigated by the c.p.-d.d.-m.a.s. 13 C-n.m.r. technique. The chemical shifts of the signals of C-1 and C-6 provide information about conformation and the results agree fairly well with the earlier scattering data on hydrated systems, but some discrepancies have been found for cyclomaltohexaose. Th conformation of the macro-rings seems to be determined by the hydration water. The unique role of water in forming crystals of cyclomalto-oligosaccharides is demonstrated.

Experimental proof for nanoparticle origin of photoluminescence in porous silicon layers

A series of nonlinear phenomena in the excitation intensity dependence of photoluminescence (PL) was observed in porous silicon (PS) at room temperature. From a low level of excitation, the blue shift of the PL spectra was detected followed by complete saturation of the integrated PL intensity, without detectable change in the spectral position. This behavior may well be experimental proof of the nonparticle origin of PS light emission.

1H nuclear magnetic resonance study of intervertebral discs. A preliminary report.

In vitro ¹H pulse nuclear magnetic resonance (NMR) studies on human intervertebral disc tissues were performed to establish the characteristics of relaxation processes. The spin-lattice relaxation time, bound water and dry matter content were measured. Biopsy material from fresh cadavers was taken from different discs along the spinal column and from different sectors of some single discs. It is suggested that the measured parameters correlate with the biomechanical behavior of discs, which in turn is influenced by function, by exposure to physical stresses, or by aging.