Knowledge Bank

“The infrared stimulated emission from an ultraviolet sensitized rigid glass solution recently $reported1,2$ has been quantitatively analyzed. The system consists of a carefully degassed rigid dilute solution of $N,N,N\prime ,N\prime$ -tetramethylparaphenylendiamine (TMPD) in 3-methylpentance at $77\circ K$. After photoionization with ultraviolet light luminescence can be stimulated with low energy radiation. It is found that the spectrum of the infrared stimulated emission can be accurately reproduced by taking the fluorescene band and phosphorescence band stimulated by primary excitation (near ultraviolet) in a proportion of one part fluorescence to 6.6 parts phosphorescence. Modulation techniques permit the resolution of the time dependent stimulated emission signal into its two components each having its won time dependence. The fluorescence component reflects the recombination kinetics while the phosphorescence component reflects as mixture of recombination kinetics and intrinsic life-time. An analysis of the time dependence is possible which yields the observed phosphorescence life time for TMPI) in this environment. The analysis is carried out for stimulating frequencies at $590m\mu$ and $546m\mu$ as well as near infrared. The correct lifetime of the phosphorescence is recovered in each case. However a strong dependence on stimulating frequency of the relative intensities of the tow components is observed. Finally, the recombination Kinetics are not easily analyzed except when stimulating at $546m\mu$ where second orders kinetics hold well for at least 80% of the total emission. The study lends strong support to the proposal that the low energy stimulated emission originates with the photoionization of a shallowly trapped electron followed by a radiative recombination with a previously photoionized solute molecule.”