transition (4 f
6
5 d
1
/4f
7
) centered at around 420 nm. The absolute
PL emission intensities from the samples made either in air or N
2
showed a similar trend as shown in Fig. 1, namely, the PL intensity
increased with the increasing Eu percentage concentration and
reached a maximum for 1% mol Eu samples before it went down.
Furthermore, as shown in Fig. 3 , a shif t to longer PL emission
wavelength for air vs. N2
was obvious for the 1% Eu samples, which
was less obvious for the lower doping samples. This suggests that
different atmosphere may affect the electronic environment sur-
rounding an europium activator, which may affect the intrinsic
luminescence.
To investigate X-ray storage and the subsequent photo-
stimulation, PSL stimulation spectra were recorded from both sets
of samples.Fig. 4 shows the normalized PSL stimulation spectra as a
function of Eu concentration. The spectra were independent of the
fabrication atmosphere. Besides the well-known F-center centered
at 560 nm, no other stimulation peak was observed. There was no
change i n the spectral shape and their full-width-at-half-maximum
(FWHM), suggesting that activator concentration and fabrication
atmosphere were not perturbing the chloride based vacancies,