Self-trapped exciton luminescence induced in alpha quartz by swift heavy ion irradiations

Natural quartz single crystals (alpha-SiO2) have been exposed to pulsed hea vy ion beams (C-12, F-19, S-32) with energies of 1 MeV amu(-1) in the elect ronic slowing down regime. The simultaneous recording of the ion fluence an d emitted photons with time-resolved spectroscopy experiments allowed the m easurement of the "blue luminescence" time decay at 85 K as a function of t he fluence at the various electronic stopping power, S-e=(-dE/dx)(e), of th e ions. For all ions, regardless of fluence, the spectra are similar and ha ve two broad bands centered at 1.60 and 2.75 eV with full widths at half ma ximum around 0.30 and 0.75 eV, respectively. Single-exponential time decay curves are found regardless of S-e increasing from 1.4 keV nm(-1) (12 MeV C -12) to 5.2 keV nm(-1) (32 MeV S-32) across the amorphous track-formation t hreshold at 2.5 +/- 0.5 keV nm(-1). At low damaged fractions (less than or equal to 22%), the decay-time constant ranges between 1.0 and 1.6 ms. The l uminescence intensities at zero delay time approximately decrease in an exp onential fashion versus fluence with a decay cross section increasing by ar ound one order-of-magnitude at the track-formation threshold, as found in t he previous experiments with continuous beams. We analyze to which extent t he luminescence decay versus fluence could be due to the quenching of the s elf-trapped exciton (STE) radiative recombinations by interactions with the ion-induced defects. For this, a STE diffusion model is devised where the STEs recombine nonradiatively at the neighboring cylindrical tracks. The mo del gives luminescence decay curves versus fluence in good agreement with t he experimental data by varying the STE diffusion constant and the amorphou s track-core radius in a reasonable range of values. (C) 2000 American Inst itute of Physics. [S0021-8979(00)08312-2].