Physical Chemistry - Lab Report Example

Download file to see previous pages... Chemical electronic transitions that are usually induced through the absorption of visible light spectrum result in excited state molecules. In the process energy is absorbed, dissipated or both. The absorbed energy must be released to return the excited species back to the original ground state. Typically, on absorption of light at their absorption maxima, dye molecules exhibit long excited state lifetimes and emit radiation at longer wavelengths (fluorescence or phosphorescence). The excited state of the luminescent dye can be quenched by an energy transfer mechanism upon collision with oxygen molecules [1]
As a result, the intensity of luminescence is reduced along with the lifetime and the degree of quenching is proportional to the oxygen concentration. Fig. 1 shows a schematic diagram of an optical oxygen sensor. The active components of the sensor are the luminescent dye encapsulated in a polymer medium, a light source (commonly a LED or laser) for exciting the dye at a particular wavelength, (550–800 nm) [2], a photodiode to detect the fluorescent radiation and an optical fiber for the transmission of light. The quenching of the luminescence can be characterized by the Stern-Volmer eqn. [3]
Figure 1 Schematics of an optical oxygen sensor. (1) Gas or liquid path, (2) Lumophore dispersed on oxygen permeable membrane, (3) lens and filter, (4) exciting radiation, (5) fluorescent radiation, (6) optical fiber, (7) LED/Laser, (8) photodiode, and (9) display
In a typical ground electronic state is a singlet (all electrons paired). Electronic excitation results in an excited state singlet that may undergo internal conversion to a triplet state. Due to the forbidden nature of a triplet singlet transition, the triplet state may exist for a substantial length of time. The emission from this state is known as the phosphorescence. Fluorescence refers to the emission from ...Download file to see next pagesRead More