Knowledge Bank

The $Tt\leftarrow S0$ absorption spectra of single crystals of naphthalene doped with a phosphorescent impurity have been obtained using photoexcitation techniques. The resolution is sufficiently high to clearly reveal the Davydov splitting of the vibronic bands. The photoexcitation spectrum of a single crystal 4 mm long shows more than 15 vibronic bands with a signal to noise ratio of the strongest band (the 0.0) of about 40 to 1. This is to be compared to the direct absorption of a crystal 40 mm long which only reveals 5 vibronic bands with a signal-to-noise ratio of approximately 4 to 1 for the $0,0$.