Spectra solid state fluorescence

Lasers produce spatially narrow and very intense beams of radiation, and lately have become very important sources for use in the UV/VIS and IR regions of the spectrum. Dye lasers (with a fluorescent organic dye as the active substance) can be tuned over a wavelength range of, for instance, 20-50 nm. Typical solid-state lasers are the ruby laser (0.05% Cr/Al203 694.3 nm) and the Nd YAG laser (Nd3+ in an yttrium aluminium garnet host 1.06 pm). 

Figure 2.5. Energy level diagram (top) and spectra (bottom) illustrating the two-state model of relaxation. The energy of the absorbed quantum is Av , and the energies of the emitted quanta are hvfl (unrelaxed) and hvF (relaxed). The fluorescence spectrum of the unrelaxed state (solid curve) is shifted relative to the absorption spectrum (dotted curve) due to the Stokes shift. The emission intensity from the unrelaxed state decreases and that from the relaxed state (dashed curve) increases as a result of relaxation.

Most of the solid-state lasers employ as active material crystals or glasses doped with rare-earth or actinide ions, because these ions exhibit a large number of relatively sharp fluorescent lines, covering the whole visible and near-infrared spectrum 380) search for new laser materials and investigations of the characteristics of laser emission at different temperatures of the active material and with various pump sources have improved knowledge about the solid state spectra and radiationless transitions in laser media 38i). 

Certain compounds, whether present in solution or in solid state (as molecular or ionic crystals) emit light when they are excited by photons in the visible or near ultraviolet domain of the spectrum. This phenomenon, called luminescence, is the basis of fluorimetry, a very selective and sensitive analysis technique. The corresponding measurements are made with fluorimeters or spectrofluorimeters and, for chromatographic applications, with fluorescence detectors. 

Excimer emission (460 nm) is observed from crystalline 16 at -186°C, but not at room temperature or in a methylcyclohexane glass (60). Photodimerization in the solid state results in a decrease in excimer fluorescence intensity and the appearance of monomer emission. Evidently, solid state photodimerization results in the isolation of monomer molecules among the dimers, as has been observed with anthracenes (65). The absorption spectrum of polycrystalline 16 is broader than the solution spectrum but the long-wavelength maximum (300 nm) is unchanged. 

The laser emission peak from R6G doped ORMOSIL gels occurred at 571 nm with a bandwidth of 4 nm. The laser emisison band is narrower than the FWHM fluorescence band. The doped ORMOSIL sample exhibited a luminescence peak at 565 nm with a bandwidth of 55 nm (FWHM) In contrast to the C153 gel, the solid state rhodamine doped sample did not oscillate over the FWHM range of die fluorescence emission spectrum. The R6G samples exhibited detectable oscillation over a total range of about 38 nm (559 to 587 nm). 

The prism at the outlet of the laser serves to separate the laser emission of the gas fluorescence and allows for a clean excitation of the sample. For excitation using solid-state lasers, this element is dispensable. The lens (element 5) collects the fluorescent signal and focuses on the aperture of the monochromator. The filter is used to eliminate excitation that is spread over the surface of the sample. The optical chopper serves to modulate the light at a defined frequency, which serves as reference for the lock-in amplifier. A data acquisition system controls the pace of the monochromator and reads the signal of the lock-in, generating the sample s emission spectrum. 

Figure 15-15. Time-resolved dispersed fluorescence (TRDF) spectra of PdG in room-temperature aqueous solution at the excitation wavelength of (a) 280 nm and (b) 300 nm. The time gates are 0-100 ps circles) and 0-6.0 ns (squares) in the fluorescence decay. The steady-state spectrum (solid line) of PdG in aqueous solution is also shown for comparison (not scaled to the ordinate). (Reprinted with permission from Ref. [24].)...

The emission spectrum of 9 TCP has been studied revealing a CT fluorescence both in the solid state and in nonpolar rigid solution at - 196 C, but not in fluid solution (74BCJ442). The CT complex 9 TCP in the solid state shows exclusively a CT fluorescence, the emission from the component ions being completely quenched. 

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