  We investigate the influence of X-ray and gamma-ray irradiation on the
photophysical properties of sub-monolayer CdTe/CdS quantum dots (QDs)
immobilized in porous silica (PSiO2) scaffolds. The highly luminescent QD-PSiO2
thin films allow for straightforward monitoring of the optical properties of
the QDs through continuous wave and time-resolved photoluminescence
spectroscopy. The PSiO2 host matrix itself does not modify the QD properties.
X-ray irradiation of the QD-PSiO2 films in air leads to an exponential decrease
in QD emission intensity, an exponential blue-shift in peak emission energy,
and substantially faster exciton decay rates with increasing exposure doses
from 2.2 Mrad(SiO2) to 6.6 Mrad(SiO2). Gamma-ray irradiation of a QD-PSiO2 thin
film at a total exposure dose of 700 krad(SiO2) in a nitrogen environment
results in over 80% QD photodarkening but no concurrent blue-shift in peak
emission energy due to a lack of photo-oxidative effects. Near-complete and
partial reversal of irradiation-induced photodarkening was demonstrated on
X-ray and gamma-ray irradiated samples, respectively, through the use of a
surface re-passivating solution, suggesting that there are different
contributing mechanisms responsible for photodarkening under different
irradiation energies. This work contributes to improving the reliability and
robustness of QD based heterogeneous devices that are exposed to high risk,
high energy environments with the possibility of also developing QD-based large
area, low-cost, re-useable, and flexible optical dosimeters.
