[Application of wavenumber-linear scaling to the calculated Raman frequencies of polyenes and carotenoids].

Raman spectra of two typical carotenoids (beta-carotene and lutein) and some short (n = 2-5) polyenes were calculated using density functional theory. The wavenumber-linear scaling (WLS) and other frequency scaling methods were used to calibrate the calculated frequencies. It was found that the most commonly used uniform scaling (UFS) method can only calibrate several individual frequencies perfectly, and the systematic result of this method is not very good. The fitting parameters obtained by the WLS method are upsilon(obs)/upsilon(calc)) = 0.999 9-0.000 027 4upsilon(calc) and upsilon(obs)/upsilon(calc)= 0.993 8-0.000 024 8upsilon(calc) for short polyenes and carotenoids, respectively. The calibration results of the WLS method are much better than the UFS method. This result suggests that the WLS method can be used for the frequency scaling of the molecules as large as carotenoids. The similar fitting parameters for short polyenes and carotenoids indicate that the fitting parameters obtained by WLS for short polyenes can be used for calibrating the calculated vibrational frequencies of carotenoids. This presents a new frequency scaling method for vibrational spectroscopic analysis of carotenoids.

[Research on the spectral properties of the Rhodamine 101 dye].

The absorption, fluorescence and time-resolved fluorescence spectra of Rhodamine 101 dye in both methanol and acidic methanol solutions were measured. The authors achieved the characteristic information of the absorption and fluorescence spectra, and obtained the S1 lifetimes. The authors assigned vibrational modes of the Rhodanmine 101 dye molecule through spontaneous Raman spectrum, infrared spectrum, and density function theory calculation. This work systemically characterizes the spectral, molecular structural, and vibrational information of Rhodamine 101 dye molecule, and provides necessary information for the application of Rhodamine 101 dye in dye sensitized solar cell and biological fluorescence marker.

Two-photon-excited luminescence in a Tb3+ -doped lithium niobate crystal pumped by a near-infrared femtosecond laser.

Blue (487.6 nm), green (544.1 nm), yellow (582.1 nm), and red (623.6 nm) upconversion (UC) luminescences are achieved in a Tb(3+)-doped lithium niobate crystal when an 800 nm femtosecond laser is loosely focused onto the sample at room temperature. The relationship between UC luminescence intensity and the pump energy indicates that a two-photon excitation process is dominant in this UC luminescence phenomenon. The Tb(3+) sensitive temperature dependence of the luminescence intensity is demonstrated via an obvious reduction of luminescence intensity with durative laser irradiation.

Enhanced green upconversion emission of Er(3+) through energy transfer by Dy(3+) under 800 nm femtosecond-laser excitation.

Er(3+) green upconversion (UC) emission corresponding to the transition of (4)S(3/2) ((2)H(11/2))-->(4)I(15/2) is enhanced in a Er/Dy-codoped LiNbO(3) crystal compared with Er-doped LiNbO(3) under 800 nm femtosecond-laser excitation at room temperature. The upconversion mechanisms are proposed based on spectral, kinetic, and pump-power dependence analyses. The energy-transfer efficiency from Dy(3+)((4)F(9/2)) to Er(3+)((4)F(7/2)) is 33%, which results in the enhancement of green UC emission. This energy transfer is advantageous for the Er(3+) UC emission sensitized by Dy(3+), especially in a low-phonon-energy host matrix.

Effect of pressure and solvent on Raman spectra of all-trans-beta-carotene.

The ground state Raman spectra of all-trans-beta-carotene in n-hexane and CS2 solutions are measured by simultaneously changing the solvent environment and molecular structure under high hydrostatic pressure. The diverse pressure dependencies of several representative Raman bands are explained using a competitive mechanism involving bond length changes and vibronic coupling. It is therefore concluded that (a) the in-phase C=C stretching mode plays an essential role in the conversion of energy from S1 to S0 states in carotenoids, (b) internal conversion and intramolecular vibrational redistribution can be accelerated by high pressure, and (c) the environmental effect, but not the structural distortion or pi-electron delocalization, is responsible for the spectral properties of a given carotenoid species. These findings revealed the potential of high pressure in exploring the nature of the biological functions of carotenoids.