Visualizing cation vacancies in Ce:Gd₃Al₂Ga₃O₁₂ scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Abstract

To clarify the existence of cation vacancies in Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPALS spectra of GAGG and Ce:GAGG comprised two exponential decay components due to positron annihilation at bulk and defect states. By an analogy with Ce:Y3Al5O12, the defect-related component was attributed to Al/Ga–O divacancy complexes. This component was weaker for Ce,Mg:GAGG, which correlated with the suppression of electron traps responsible for phosphorescence. O vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was changed by Mg co-doping. This was explained by the formation of vacancy clusters.

Subsurface oxygen defects electronically interacting with active sites on In2O3 for enhanced photothermocatalytic CO2 reduction

“…Compared with In 2 O 3 , In-Em In 2 O 3 displays a longer third lifetime (τ 3 ), reflecting defect accumulation at the interface. The first component is attributed to free annihilation of the positrons by a bulk state in a crystal 36,37 . The dissimilarity of the first lifetimes (τ 1 ) between In 2 O 3 and In-Em In 2 O 3 is only 9 picoseconds, attributable to small vacancies 38,39 or shallow positron traps 40 TOF activity over In-Em In 2 O 3 is 866 times higher than that over In 2 O 3 under light irradiation.…”

“…The positron trapping rates were calculated, which is proportional to the number of defects and density of negative charges in an individual defect. The positron trapping rate is directed against the second component exclusively pertaining to defects 37 . As shown in Supplementary Figs.…”

Crystal growth and scintillation properties of tube shape-controlled Ce-doped Y3Al5O12 single crystals grown by micro-pulling-down method

“…1) Scintillators have also been used for imaging in nuclear medicine, especially for positron emission tomography 2,3) and many other studies that are being actively carried out. 4,5) Recently, imaging methods where a scintillator array serves as a collimator have been developed. 6,7) Simultaneous radiation detection with a wide range of energy could be achieved, which was a significant challenge for such imaging methods.…”

Subsurface Oxygen Defects Electronically Interacting with Active Sites on In2O3 for Enhanced Photothermocatalytic CO2 Reduction

“…Compared with In 2 O 3 , In-Em In 2 O 3 displays the longer third lifetime, re ecting defect accumulation at the interface. The rst component is attributed to free annihilation of the positrons by a bulk state in a crystal [37][38] . The dissimilarity of the rst lifetimes between In 2 O 3 and In-Em In 2 O 3 is only 9 picoseconds, attributable to small vacancies [39][40] or shallow positron traps 41 activity/number of active sites, see methods) under identical light intensity (866-fold) and identical reaction temperature (376-fold) (Fig.…”

“…The positron trapping rate were calculated, which is proportional to number of defects and density of negative charges in an individual defect. The positron trapping rate is directed against the second component exclusively pertaining to defects 38 . As shown in Supplementary Figs.…”