Reviewing the effect of aggregates in Rhodamine 6G aqueous solution on fluorescence quantum efficiency.

Rhodamines constitute a class of dyes extensively investigated and applied in various contexts, primarily attributed to their high luminescence quantum yield. This study delves into the impact of aggregation on the thermal and optical properties of Rhodamine 6G (R-6G) solutions in distilled water. Examined properties encompass thermal diffusivity (D), temperature coefficient of the refractive index (dn/dT), fluorescence quantum efficiency (η), and energy transfer (ET). These parameters were assessed through thermal lens (TL) and conventional absorption and emission spectroscopic techniques. The dimerization of R-6G solutions was revisited, revealing that an increase in R-6G concentration alters the features of absorption and emission spectra due to dimer formation, resulting in unexpected behavior of η. Consequently, we introduce a novel model for the fraction of absorbed energy converted into heat (φ), which accounts for emissions from both monomers and dimers. Employing this model, we investigate and discuss the concentration-dependent behaviors of η for monomers (ηm) and dimers (ηd). Notably, our findings demonstrate that ηm values necessitate ηd = 0.2, a relatively substantial value that cannot be disregarded. Additionally, applying the Förster theory for dipole-dipole electric ET, we calculate microparameters for ET between monomers (CDD) and monomer-dimer (CDA). Critical ranges for ET in each case are quantified. Microparameter analysis indicates that ET between monomer-monomer and monomer-dimer species of R-6G dissolved in distilled water holds significance, particularly in determining ηm. These results bear significance, especially in scenarios involving high dye concentrations. While applicable to R-6G in water, similar assessments in other media featuring aggregates are encouraged.

Towards a comprehensive characterization of spatio-temporal dependence of light-induced electromagnetic forces in dielectric liquids.

The interaction of localized light with matter generates optical electrostriction within dielectric fluids, leading to a discernible change in the refractive index of the medium according to the excitation's light profile. This optical force holds critical significance in optical manipulation and plays a fundamental role in numerous photonic applications. In this study, we demonstrate the applicability of the pump-probe, photo-induced lensing (PIL) method to investigate optical electrostriction in various dielectric liquids. Notably, the thermal and nonlinear effects are observed to be temporally decoupled from the electrostriction effects, facilitating isolated observation of the latter. Our findings provide a comprehensive explanation of optical forces in the context of the recently introduced microscopic Ampère electromagnetic formalism, which is grounded in the dipolar approximation of electromagnetic sources within matter and characterizes electrostriction as an electromagnetic-induced stress within the medium. Here, the optical force density is re-obtained through a new Lagrangian approach.

Optical detection of the ultrasound-induced pulsed thermal lens close to the ice-water phase transition.

Piezo-optic and thermo-optic coefficients are important material properties that play a critical role in the design and optimization of many optical devices. The ability to accurately measure and control these coefficients is essential for achieving high performance and reliability in a wide range of applications. In this article, we use the optical detection of the ultrasound-induced thermal lens effect to investigate these properties for water at low temperatures. The results show that the anomalous behavior of water around 4°C is easily observed. The thermal lens method is used to determine the temperature dependence of the piezo-optic and thermo-optic coefficients.

Diffusion Processes and Drug Release: Capsaicinoids - Loaded Poly (ε-caprolactone) Microparticles.

We present a generalmodel based on fractional diffusion equation coupled with a kinetic equation through the boundary condition. It covers several scenarios that may be characterized by usual or anomalous diffusion or present relaxation processes on the surface with non-Debye characteristics. A particular case of this model is used to investigate the experimental data obtained from the drug release of the capsaicinoids-loaded Poly (ε-caprolactone) microparticles. These considerations lead us to a good agreement with experimental data and to the conjecture that the burst effect, i.e., an initial large bolus of drug is released before the release rate reaches a stable profile, may be related to an anomalous diffusion manifested by the system.

Pulsed photothermal mirror technique: characterization of opaque materials.

The time-resolved thermal mirror technique is developed under pulsed laser excitation for quantitative measurement of thermal and mechanical properties of opaque materials. Heat diffusion and thermoelastic equations are solved analytically for pulsed excitation assuming surface absorption and an instantaneous pulse. Analytical results for the temperature change and surface displacement in the sample are compared to all-numerical solutions using finite element method analysis accounting for the laser pulse width and sample geometry. Experiments are performed that validate the theoretical model and regression fitting is performed to obtain the thermal diffusivity and the linear thermal expansion coefficient of the samples. The values obtained for these properties are in agreement with literature data. The technique is shown to be useful for quantitative determinations of the physics properties of metals with high thermal diffusivity.

The phase-resolved photoacoustic method to indicate chemical assignments of paracetamol.

In this work, the phase-resolved photoacoustic method was applied to provide specific information on the chemical assignments of paracetamol in the near-infrared region. Two broad bands, centered at 1370 and 1130 nm, were well-resolved using this method, making it possible to assign the peaks centered at 1398, 1355 and 1295 nm to a C-H combination from a CH3 structure and the peak at 1305 nm to a C-H combination from the aromatic ring. This information represents a new finding in chemical studies regarding this medicament.

High values of gain cross section and luminescence quantum efficiency in OH(-)-free Ti3+-doped low-silica calcium aluminosilicate glass.

We recently reported that Ti(3+)-doped low-silica calcium aluminosilicate glass presents long luminescence lifetime (170 micros) and broad emission band (190 nm) shifted toward the visible region when compared with those from Ti(3+):sapphire single crystal and Ti(3+)-doped glasses [Phys. Rev. Lett.100, 027402 (2008)]. Here we demonstrate that this glass also shows high values of both gain cross section (approximately 4.7 x 10(-19) cm(2)) and luminescence quantum efficiency (approximately 70%). By comparing these values with those for Ti(3+):sapphire crystal, we can conclude that the studied Ti(3+)-doped glass is a promising system for tunable solid-state lasers.

Long fluorescence lifetime of Ti3+-doped low silica calcium aluminosilicate glass.

This Letter reports the formation of Ti3+ in OH- free aluminosilicate glass melted under vacuum condition, with a very long lifetime (170 micros) and broad emission band shifted towards the visible region. This lifetime value was attributed to the trapping of the excited electrons by the glass defects and detrapping by thermal energy, and it is 2 orders of magnitude higher than those published for Ti3+ doped materials. Our results suggest that this glass is a promising system to overcome the challenge of extending the spectral range of traditional tunable solid state lasers towards the visible region.