High-resolution luminescence of epitaxial organic films: quaterthiophene on Ag(111)

Thin films (less than 40 Å) of quaterthiophene (4T) were vapour deposited onto a Ag(111) surface under ultrahigh vacuum (UHV) and were investigated concerning their geometrical structure and photoluminescence (PL) properties by low-energy electron diffraction (LEED) and optical spectroscopy, respectively. Two different structural phases (α and β) were observed, which exhibit high structural order, with crystalline domains that are oriented with respect to the Ag(111) surface. Phase α is formed if 4T is deposited onto a 200 K cold Ag surface; phase β forms after an additional annealing step at 300 K. Due to the high order, the PL spectra of both phases show very narrow lines (phase β: FWHM0-0 ≤ 40 cm−1) and highly resolved fine structures, which are discussed in detail. In comparison with 4T films on glass, PL efficiency of phase β is larger by a factor of at least five.