The unusually intense luminescence (commonly called triboluminescence)
observed when opening self-seal envelopes has been studied using
the major cause of the intense blue luminescence (around 435 nm) is
attributed to optical brightening agents added to the white paper.
The results suggest that the emission from the brightening agents may be
caused by two mechanisms: (i) fluorescence due to excitation by the UV
light from the gas discharge and (ii) nonoptically, by electron
transfer. The electrical discharge results from contact
electrification; a mechanism was proposed for the charge transfer
involving a net
migration of hydroxide anions out of the paper into the wet
latex-adhesive during drying.