Vibrationally Resolved Fluorescence from Organic Molecules near Metal Surfaces in a Scanning Tunneling Microscope Z.-C. Dong,1 X.-L. Guo,1 A. S. Trifonov,1 P. S. Dorozhkin,1 K. Miki,1 K. Kimura,1 S. Yokoyama,2 and S. Mashiko2 1 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 2 Communication Research Laboratory, Kobe, Hyogo 651-2401, Japan (Received 11 September 2003; published 24 February 2004)    Intrinsic molecular fluorescence from porphyrin molecules on Au(lOO) has been realized by using a nanoscale multimonolayer decoupling approach with nanoprobe excitation in the tunneling regime. The molecular origin of luminescence is established by the observed well-defined vibrationally resolved fluorescence spectra. The molecules fluoresce at low "turn-on" voltages for both bias polarities, suggesting an excitation mechanism via hot electron injection from either tip or substrate. The excited molecules decay radiatively through Franck-Condon π*-π transitions. DOI: 10.1103/PhysRevLett92.086801       PACS numbers: 68.37.Ef, 33.50.-j, 73.20Mf, 73.21.Ac