Knowledge Bank

Known thicknesses of solid nitrogen (between 2 and 1000 nm) are deposited on substrates cooled to 15K in an ultrahigh vacuum system. The nitrogen it excite by a weak pulse of 3KeV and the $N2D$ $\to 4S$ lifetime measured. The radiative $N2$D$\to 4S$ lifetime varies from 37 seconds for very thick nitrogen films to less than 1 seconds for very thin nitrogen films. The radiative lifetime in also substrate dependent. Thin films of solid nitrogen on a sapphire substrate have much longer lifetimes and higher relative quantum efficiencies than do thin nitrogen films on a silver substrate. Thin nitrogen films on thin evaporated silver films over sapphire have even shorter lifetimes and lower quantum efficiencies.