Thermal decomposition, laser effect

Thermal decompositions have been studied most effectively by mass spectroscopic thermal analysis, thermogravimetric analysis, and electrical conductivity. Several analytical characterizations of phenolic resins have recently been reported, making use of a variety of properties, including expansion coefficients, " specific heat capacity, ultrasonic properties, dipole moments, and laser light scattering. Recently, high-temperature properties of reinforced phenolic components have been studied by Goetzel. ... 

Experiments are performed behind reflected shock waves where the hot gas is effectively stagnant and not flowing. Flash or laser photolysis occurs after the reflected shock wave has traversed the spectroscopic observation station. Transient species are observed radially across the shock tube. Reflected shock pressure and temperature are kept low so that thermal decomposition is minimized. The initial transient species concentration is initiated by photolysis, and its decay is then totally determined by bimolecular reaction. Diffusion out of the viewing zone is negligibly slow on the experimental time scale. This experiment is then an adaptation of the static kinetic spectroscopy experiment with the reflected shock serving as a source of high temperature and density i. e., shock heating is equivalent to a pulsed furnace. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Laser lUman spectroscopy (LRS). The spectra were recorded on a Nicolet 950 FT-Raman spectrometer instrument, equipped with a nitrogen cooled Ge detector. A Nd YAG laser (1064 nm) was used as excitation source. The measurements were performed with a power at the sample of 100-200 mW in order to avoid decomposition and thermal effects. The samples were rotated to provide a noncontinuous irradiation of any given spot on the samples. The spectral slit width was typically 4 cm". ... 

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