the adsorbed water content, the batches of 4 g were weighed and
stored in a vacuum furnace at 100 1C. A homogeneous mixture was
heated in a protective atmosphere of dried argon. Glasses were
melted at 900 1C in Pt crucibles, then poured into pre-heated
copper moulds and annealed below the glass transition temperature.
After this procedure, the samples were slowly cooled to the
room temperature. Transparent glassy plates were obtained with
thickness of about 2 mm.
The actual content of Cl ions has not been estimated. However,
the final glass compositions are somewhat different from the
nominal starting ones because of the amount of gases lost during
the melting processes due to the following reaction: PbCl2+H2OPbO+2HClm.
Analytical studies of the other mixed oxyhalide glass
systems revealed that the fluorine [33] or chlorine [34] losses could
be quite large. Recently, the fluorine retention in oxyfluoride
silicate glasses was examined as a function of glass composition
[35]. The obtained results clearly demonstrated that the fluorine
losses monotonically increased with increasing initial PbF2 content.
In order to minimize PbX2 losses, the relatively low concentration
of fluorine or chlorine components in the mixed oxyhalide
samples is suggested. This is the main reason why our glass
samples have a small amount of PbCl2 in their compositions.
Luminescence was measured with a Continuum Model Surelite I
OPO pumped by a third harmonic of a Nd:YAG laser. Emission
spectra were recorded using a Stanford SRS 250 boxcar integrator
controlled by a computer. The spectral resolution was 70.2 nm.
Decay curves were recorded and stored by a Tektronix TDS 3052
oscilloscope with an accuracy of 70.5 ms.