Phosphorimetric Methods In Chemical Analysis:

Previously you learnt that Phosphorescence has been observed from a huge variety of compounds and is differentiated from fluorescence through the long-lived emission of light after extinction of the excitation source.  In comparison to the fluorescence methods, the phosphorimetric methods are not much used for analytical reasons. The applications of phosphorescence have been somewhat limited in the past because of the lack of appropriate instrumentation.  Another impediment in the extensive usage of phosphorescence is the practical difficulty within measuring the signal, because the measurements are to be made at cryogenic temperatures. It is commonly essential to freeze the sample, taken in special solvents, using liquid nitrogen.

The problem is additional augmented through the fact that in comparison to fluorescence, the phosphorescence life time is much larger whereby the molecule has a extremely high probability of losing its excess energy through radiationless processes such as, bimolecular collision, internal conversion, and photodecomposition, etc. Conclusion, phosphorescence is not routinely observed in solutions at room temperature. This is measured within viscous media or from molecules adsorbed on solid surfaces while these nonradiative processes are minimized or deactivated. Oxygen also promotes radiationless deactivation of the triplet state and is effective in preventing phosphorescence.  Thus, a thorough degassing of the solution is needed before measurement.

On the other hand with the introduction of new instrumental methods and the advances made in room temperature phosphorescence, phosphorimetry is poised to make huge leaps in the domain of clinical chemistry and in the areas of forensic, environmental and pharmaceutical sciences. Now let us learn about room temperature phosphorescence.