Maurice W. Windsor

Internal‐Energy‐Transfer Efficiencies in Eu3+ and Tb3+ Chelates Using Excitation to Selected Ion Levels

Fluorescence yields of solutions of several chelates of europium and terbium have been measured: (a) upon excitation in the ligand absorption bands and (b) upon selective excitation to individual upper levels of the rare‐earth ion. Yields with upper‐ion‐level excitation are lower than when the emitting level is excited directly and yields with ligand excitation are lower still. Efficiencies of energy transfer to the emitting level from upper ion levels and from the ligands, for the solutions studied, are calculated from the data.The fluorescence yield observed when the emitting level is excited directly, together with the fluorescence lifetime, allows both radiative and radiationless rate constants for deactivation of the emitting level to be calculated. The enhanced fluorescence yields of chelates compared to unchelated rare‐earth ions are found to be due primarily to the enhancement of the radiative transition by the chelate environment rather than to a protective influence against quenching provided by...

The Triplet State in Fluid Media

Absorption spectra of the triplet states of a variety of organic molecules have been observed in fluid solutions at normal temperatures. Triplet-triplet spectra are given for thirty-two molecules and, for ten of these, absolute extinction coefficients and oscillator strengths have been measured. In most cases several distinct electronic transitions have been found and the energy levels and oscillator strengths of these transitions are compared with the results of molecular orbital calculations for the first five linear polyacenes. Triplet-state lifetimes have been measured for naphthalene and anthracene in a wide range of solvents and the effect of dissolved gases, particularly oxygen, on these lifetimes is described.

An Eye Protective Panel for Flash-Blindness Protection Using Triplet State Photochromism

A photochromic panel is described which has a viewing area of 15.0 cm x 20.0 cm and a thickness of 6.0 cm. It includes two photochromic plates of epoxy plastic containing four aromatic hydrocarbon compounds which are excited to their triplet states with two xenon flashlamps. The triplet absorption of the aromatic compounds results in a photochromic absorbance of 2.42 when the panel is activated with a 3000-J flash; 85% of the final absorbance is achieved 150 microsec after the beginning of the flash. The transmission of the panel recovers to 37% 5 see after the panel darkens. The open-state transmission of the panel is 83%.