M. Ambrož

Spectral hole burning of photosynthetic antenna of blue-green algae

Photosystem II core antenna of blue-green algae Synechococcus isolated in gel was studied by optical hole burning spectroscopy at 4·2 K. Persistent holes were burned into fluorescence spectra throughout the region 680–696 nm. The hole width extrapolated to zero burning fluence yielded a value 1·0±0·2 cm−1. A theoretical interpretation of the hole profile in fluorescence is presented. The dependence of saturated hole depth on burning wavelength is related to inhomogeneous site distribution function.

Luminescence of direct-and indirect-gap electron-hole plasma in TlBr

Abstract Luminescence of TlBr crystals highly excited by a nanosecond pulsed-dye laser (3.4 eV) at the bath temperature ∼ 8.5 K was studied. Two emission lines labeled A (∼ 2.98 eV) and B (∼ 2.62 eV) were found, which show typical behavior of the electron-hole plasma recombination radiation. The A-line is assigned to the recombination of e-h pairs in the direct gap ( X + 6 − X - 3 ) and the B-line to the simultaneous recombination in the indirect gap ( X + 6 − R - 6 ). Condensation of carriers into an electron-hole liquid was not observed.

Influence of water stress on photosynthesis and variable chlorophyll fluorescence of potato leaves

Net photosynthetic rate (PN), productivity and the first phases of the fluorescence induction curve were investigated in leaves of two potato cultivars exposed to water stress. Water stress applied to potato plants at the beginning of their development (planting-bud formation) increased productivity but decreased PN and variable fluorescence (Fv) of leaves. The short-term influence of water stress on the same plants also diminished the Fv.

Photoluminescence assessment of B, P, and Al in Si wafers: The problem of sample heating by a laser beam

A line shape analysis of free‐exciton low‐temperature (4.2 K) photoluminescence spectra is applied to monitor the heating of Si samples due to an exciting Ar+‐ion laser beam. The heating is studied in dependence on the laser beam intensity. The temperature as a line shape fitting parameter can be established within ±0.15 K. Continuous minor increase of the sample temperature is observed up to an intensity of ∼200 W cm−2, followed by an abrupt temperature jump up to tens of K. Possible inaccuracies, resulting from the heating, in photoluminescent quantitative determination of boron, phosphorus, and aluminum are discussed.

Spectral hole burning study of photosynthetic antenna pigment-protein complexes

Abstract Results of persistent spectral hole burning in fluorescence spectra of photosystem II core antenna complexes CP 43 and CP 47 are presented. The holewidths (extrapolated to zero burning fluence) yield the excited state population decay times T 1 which are influenced by fast energy transfer within the antenna complexes. The obtained T 1 values range between 6.6 and 10 ps. The holewidths are independent on temperature within the studied temperature interval 1.5-4.2 K. The observed phenomenon of laser-induced hole filling in the spectra of CP 43 is explained in terms of energy transfer within the CP 43 pigment-protein complex.

Direct-indirect gap intervalley scattering of electrons in TlBr electron-hole plasma

Abstract Temperature dependence of the electron-hole plasma (EHP) radiative recombination in TlBr crystals was measured in the bath temperature range 8.5–56 K. Strong phonon-assisted competition due to intervalley electron scattering between direct and indirect gaps EHP components was found. A kinetic model is presented which explains the main features of the experiment.

Fast energy transfer in green photosynthetic bacteria Chlorobium limicola studied by spectral hole burning

Abstract Results of persistent hole burning fluorescence spectroscopy of green sulphur photosynthetic bacterium Chlorobium limicola are presented. Homogeneous spectral linewidths were determined from holewidths burned into inhomogeneously broadened NIR fluorescence spectra of chlorosomal bacteriochlorophyll-c at 1.8-4.2 K. The determined excited state relaxation time is strongly influenced by ultrafast energy transfer.

Low temperature optical spectroscopy of natural porphyrins

Abstract Low temperature hole burning excitation fluorescence spectra of a set of uroporphyrin I esters in amorphous (chloroform) matrix are presented. The hole burning spectra were excited within the region of the O-O S 1 → S 0 transition and measured in the temperature range 1.5 – 4.3 K. From the fluence the values of homogeneous linewidths were determined. The temperature dependence of the holewidth δ HB has been studied. The temperature dependence of δ HB follows the power law T α and coefficients α for uroporphyrin I esters are within the range 1.32 – 1.36, which is in good agreement with other results obtained for systems in amorphous matrices. The fluorescence lifetime values of Γ hom and zerotemperature extrapolated values are compared.

Hole burning spectroscopy of tetraphenylporphyrins

The persistent spectral hole burning technique has been applied to free base and central metal tetraphenylporphyrins with different substituents. The upper limits of the singlet-singlet homogeneous widths determined from the observed persistent holes have been correlated with the fluorescence lifetimes at low temperatures. Hole burning kinetics and mechanisms of both free base and central metal pigments are discussed.

Two-photon absorption and energy band structure of orthorhombic Hg2Cl2 crystals

Dependence of two-photon absorption (TPA) rate on the state of polarization of a laser beam is investigated in the low-temperature orthorhombic modification of Hg2Cl2 crystals. Theoretical calculations of the dependence of TPA rate on the direction of polarization vector of the beam are performed for centrosymmetric pointsγ, Y, Z, T, R andS of the Brillouin zone. The domain structure of real crystals is taken into consideration and it is shown that periodicity of the polarization dependence may indicate whether TPA is due to transitions either atγ, Y, Z, T orR, S points. The polarization dependence of TPA cannot, however, distinguish between points inside these two groups. Comparison of theory with a low-temperature (T ∼ 8·5 K) experimental curve of polarization dependence is discussed. It is shown that the experiment can be explained in main features by a model of noninteracting oriented linear dipoles. Further, on the basis of TPA measurements, a simple energy band structure of Hg2Cl2 is proposed regarding Hg2Cl2 crystal as a linear chain of molecules.