2 research outputs found
The importance of inversion disorder in the visible light induced persistent luminescence in Cr doped ABO (A = Zn or Mg and B = Ga or Al)
Cr doped spinel compounds ABO with A=Zn, Mg and B=Ga, Al
exhibit a long near infrared persistent luminescence when excited with UV or
X-rays. In addition, persistent luminescence of ZnGaO and to a lesser
extent MgGaO, can also be induced by visible light excitation via
A T transition of Cr, which makes these
compounds suitable as biomarkers for in vivo optical imaging of small animals.
We correlate this peculiar optical property with the presence of antisite
defects, which are present in ZnGaO and MgGaO. By using X-ray
absorption fine structure (XAFS) spectroscopy, associated with electron
paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown
that an increase in antisite defects concentration results in a decrease in the
Cr-O bond length and the octahedral crystal field energy. A part of the defects
are in the close environment of Cr ions, as shown by the increasing
strain broadening of EPR and XAFS peaks observed upon increasing antisite
disorder. It appears that ZnAlO, which exhibits the largest crystal
field splitting of Cr and the smallest antisite disorder, does not show
considerable persistent luminescence upon visible light excitation as compared
to ZnGaO and MgGaO. These results highlight the importance of
Cr ions with neighboring antisite defects in the mechanism of persistent
luminescence exhibited by Cr doped ABO spinel compounds.Comment: 10 pages + supplementary (available on request