Low-temperature sensibilization of naphthalene phosphorescence using ortho-bromobenzophenone

The standard approach involving the sensibilization of naphthalene phosphorescence is employed to study the mono-substituted ortho-bromobenzophenone (2-BrBP). A new feature of the approach is the use of octane as the passive neutral matrix. This matrix is chosen due to the absence of the triplet-excitation mobility in pure 2-BrBP crystal. The problem of common phosphorescence kinetics of 2-BrBP and naphthalene is solved in analytic form. Unlike in the classical problem involving unsubstituted benzophenone, the relevant phosphorescence measurements have been performed at low temperatures (as low as 1.6 K). A new approach is suggested to account for the large difference between the typical experimental pulse-delay time and the slow naphthalene phosphorescence. Relevant computations allow us to explain the nature of the two sets of phosphorescence lines of 2-BrBP.