Positron annihilation in transparent ceramics

Radiation response of Y3Al5O12 and Nd3+–Y3Al5O12 to Swift heavy ions: insight into structural damage and defect dynamics

“…Selim et al have reported t 1 in the range of 150-165 ps in YAG samples grown in various atmospheres, 49 while the bulk positron lifetime was reported to be B175 ps. 50 The lifetime (t 1 ) observed for unirradiated YAG (169 ps) in the present study is in reasonable agreement with that reported in the literature. It is reported that the positrons' lifetime in Al vacancies is about 275 ps while in Y vacancies this value is about 340 ps.…”

Physical and optical properties of Ce:YAG nanophosphors and transparent ceramics and observation of novel luminescence phenomenon

“…The presence of voids in the grain boundaries of transparent ceramics provides an array of trap levels leading to this behavior. Previous positron annihilation spectroscopy measurements by one of the authors on YAG and Ce:YAG [38,45] have confirmed the presence of large voids only in transparent ceramics samples. Fig.…”

“…Figure 4 compares the PL emission of Ce:YAG nanophosphor (annealed at 1500°C) with Ce:YAG single crystal (SC) and transparent ceramics emission recorded under the same excitation conditions. It is interesting to note that the Ce:YAG NP prepared in this work is more efficient than SC and transparent ceramics despite the excellent transparency of the Ce:YAG transparent ceramic samples [38]. No significant peak shift is observed in nanophosphor (λ max = 533nm) compared to ceramics (λ max = 532nm) and single crystal (λ max = 527nm).…”

Synergy between structural rigidity and cluster defects in a bright near-infrared Cr3+-based phosphor for excellent thermal stability and long afterglow

“…The first positron lifetime in undoped YAG is about 180 ps and is in good agreement with reported positron lifetimes of YAG based samples. 53,54 With increase in Cr 3+ doping, the first positron lifetime reduced and reached minima at about 5% doping and it increased for the 15% doped sample. The second positron lifetimes are more than 400 ps for the undoped sample and reduced with Cr 3+ doping, suggesting that the pre-existing large vacancy clusters near the surface of the particles anneal out in favour of isolated vacancies.…”