LUMINESCENCE SPECTRA OF GERMANOSILICATE OPTICAL FIBERS .2. THERMOLUMINESCENCE

Thermoluminescence spectra have been recorded for a variety of germanosilicate optical fibres over the temperature range 70 to 700 K. The signals from the small central fibre core are more intense than those from the larger substrate. Hence variations in core composition influence the spectra and glow peaks, although there are many features common to all the fibres. Activation energies of the glow peaks are reported. Emission bands are variously identified with recombination at Ge sites giving the 400 nm band, intrinsic e--h+ recombination giving the 460 nm band and rare earth dopants provide characteristic line emission. There are some examples of microcrystallites within the fibre cores. The thermoluminescence response alters slightly with irradiation dose and heating. Minor effects of drawing temperature and draw speed are noted. Overall, thermoluminescence is shown to be a sensitive monitor of impurities and imperfections within optical fibres.