High resolution spectroscopy of a small number of particles in a solid

The technique of single molecule spectroscopy in solids is investigated, with the view to extending this technique to the detection of single ions of titanium in sapphire. High-resolution experimental apparatus was set-up to study single particles in solids and to allow hole-burning experiments to be carried out. Hole-burning processes were investigated in samples of uranium doped strontium tungstate with concentrations of 500 ppm and 200 ppm. Hole-burning at different laser intensities revealed a homogeneous linewidth of (6.3 ± 0.1) MHz for the stronger doped sample. The weaker doped sample was determined to have a homogeneous linewidth less than the laser linewidth. The relaxation behaviour of holes, monitored between 10-20 K, was also examined. The relaxation process was found to be similar to an activated process with an attempt frequency of 309 s-1 and it was concluded that the process was some form of tunnelling with strong phonon coupling. Repeatable, stable single molecules of terrylene in hexadecane were measured in the wings of the inhomogeneous zero-phonon line. Unstable molecules were observed, where the molecule would jump in and out of resonance. Weakly doped crystals and films of titanium doped sapphire were found to contain strong chromium emission. The annealing of both crystals and films of titanium doped sapphire was investigated. The best procedure for obtaining films with good crystallinity and Ti3+ ions was to grow the films at 650 deg C followed by annealing at 1100 deg C in a reducing atmosphere. Hole-burning was only evident in unannealed crystals of Ti3+:AI2O3, indicating that Ti4+ is necessary for hole-burning to occur. Neither single ions or statistical fine structure were detected as the concentration of titanium ions was expected to be too large. (author)