Graphene-Based Ammonia Sensors Functionalised with Sub-Monolayer V₂O₅: A Comparative Study of Chemical Vapour Deposited and Epitaxial Graphene †.

Graphene in its pristine form has demonstrated a gas detection ability in an inert carrier gas. For practical use in ambient atmosphere, its sensor properties should be enhanced with functionalisation by defects and dopants, or by decoration with nanophases of metals or/and metal oxides. Excellent sensor behaviour was found for two types of single layer graphenes: grown by chemical vapour deposition (CVD) and transferred onto oxidized silicon (Si/SiO₂/CVDG), and the epitaxial graphene grown on SiC (SiC/EG).

Solvent Induced Transformations of n-π* Absorption in Formaldehyde, Acetaldehyde, and Acetone.

Absorption spectra of formaldehyde (FA), acetaldehyde (AA), and acetone are compared in the vapor phase, nonpolar, and polar solutions at 295 K. The vibronic n-π* transition of carbonyl chromophore is mainly composed of the overtones of >C═O stretching vibration. A new phenomenon is observed in liquid solutions, consisting of a relative increase of Franck-Condon factors for the second and third harmonics in FA, and the second to fourth replica in AA, with respect to the gas phase.

Spectral shift mechanisms of chlorophylls in liquids and proteins.

Origins of non-excitonic spectral shifts of chlorophylls that can reach -1,000 cm(-1) in pigment-protein complexes are actively debated in literature. We investigate possible shift mechanisms, basing on absorption and fluorescence measurements in large number of liquids. Transition wavelength in solvent-free state was estimated (±2 nm) for chlorophyll a (Chl a, 647 nm), Chl b (624 nm), bacteriochlorophyll a (BChl a, 752 nm), and pheophytines.

Nonlinear polarization of solvatochromic betaine 30.

Evidence is presented that solvatochromism of 2,6-diphenyl-4-(2,4,6-triphenylpyridinio)-phenolate (Reichardt's dye or Betaine 30) results not only from a large reduction of dipole moment and hydrogen bonding, but also from the modulation of mesomeric effect. The polarizability change between the ground and the excited state, estimated from the refractive index (n) dependence of absorption energy E(T)(30), increases from 20 to approximately 150 A(3) on going from apolar to highly polar media. The dependence of E(T)(30) on dielectric permittivity (epsilon) could be linearized using an empirical function of susceptibility difference (epsilon-n(2)), but not in terms of conventional expressions written as phi(epsilon)-phi(n(2)).

Solvent dependence of n-pi* absorption in acetone.

A barely resolved structure can cause considerable loss of precision when locating the maxima of broad spectra. The centers of band envelopes were determined for the acetone n-pi* absorption in vapor, pure liquid, and solutions at 293 K. A complementary method of "band-halving" is proposed for accurate measurement of solvent-induced displacements.

Influence of high pressure on optical impurity spectra.

Expressions are derived for inhomogeneous band shapes of impurity spectra in highly compressed glassy matrices. Intermolecular guest-host interactions are approximated to isotropic two-body Lennard-Jones 6-12 potentials having different parameters in the ground state and the excited state. Calculated shifts and widths are compared to published values for the absorption spectra of phenanthrene, anthracene [B.

Influence of temperature and pressure on shape and shift of impurity optical bands in polymer glasses.

The shape, broadening, and shift of optical absorption spectra of molecular impurity centers in polymer glasses are considered in terms of inhomogeneous energy distributions and coupling of electronic transitions to vibrations. Persistent spectral hole burning was applied for frequency-selective probing of zero-phonon lines. The shift and broadening of spectral holes were studied between 5 and 50 K and by applying a hydrostatic He gas pressure up to 200 bar.