Optical and Scintillation Properties of Rare-Earth Ion-Doped 12CaO·7Al2O3 Single Crystals

Abstract

We have synthesized undoped and rare-earth (RE)-doped 12CaO·7Al 2 O 3 (RE:C12A7) crystals by the floating zone (FZ) method to systematically study the effects of RE doping (doped with all the lanthanoid elements except for Sc, Y, La, Pm, and Lu) in C12A7 for radiation detector applications. In both photoluminescence (PL) and scintillation, the undoped C12A7 crystal showed a weak emission due to the lattice defects appearing at around 500 nm, and the decay time was on the order of several nanoseconds. On the other hand, the RE:C12A7 crystals showed PL and scintillation owing to the 4f-4f transitions of RE 3+ ions appearing from the UV to NIR ranges depending on the RE element. The decay times of these emissions ranged from a few microseconds to milliseconds depending on the RE element and the values were typical for the electronic transitions of trivalent rare earths.

Radioluminescence and photoluminescence properties of Dy-doped 12CaO ∙ 7Al2O3 single crystals synthesized by the floating zone method

“…Regardless of the Dy concentration, the decay time constants of Dy:C12A7 were almost the same 0.54-0.58 ms while the decay time constant of undoped C12A7 due to the lattice defects was 5.6 ns in our previous study. 23) The decay time constants of Dy:C12A7 are consistent with the results of the PL QYs. The PL decay time constants of other Dy 3+ -doped phosphor materials due to the 4f-4f transitions of Dy 3+ are about 0.140-1.56 ms, 33,[35][36][37][38][39][40][41][42][43][44] and the decay times of Dy:C12A7 were typical values of the emission due to Dy 3+ .…”

“…As in PL, only a tail part of each curve was considered in the analyses and approximated by a first-order exponential function as indicated in the figure. The obtained decay time constants were 0.49-0.53 ms regardless of Dy concentrations while the decay time component (previously reported) due to lattice defects in the undoped samples was also much faster (16.3 ns) 23) and much weaker as for PL. Moreover, PL and RL decay time constants of Dy-doped samples are approximately the same, which is not common but sometimes seen in selected materials.…”

“…The undoped sample showed a broad emission peaking around 450 nm, and the origin would be due to the lattice defects as for the PL. 23) On the other hand, Dy:C12A7 crystals showed some emission peaks due to the 4f-4f transitions of Dy 3+ . Each emission peak was ascribed to 487 ( 4 F 9=2 → 6 H 15=2 ), 580 ( 4 F 9=2 → 6 H 13=2 ), 668 ( 4 F 9=2 → 6 H 11=2 ), and 757 ( 4 F 9=2 → 6 H 9=2 ) nm.…”

“…This emission origin would be the lattice defects. 23) We also measured QY for the 0.1, 0.5, 1.0, and 2.0% Dy:C12A7 crystals upon excitation at 450 nm, and the obtained values are summarized in Fig. 4.…”

“…20) In addition to these applications, the C12A7 would also be attractive for radiation detections, especially charged particle detections due to low effective atomic number (Z eff ∼ 16.5) which is almost equivalent to that of conventional scintillators used in charged particle detectors: for example, CaF 2 (Eu) 21) (∼17.1) and ZnS(Ag) 22) (∼27.4). To date, we have systematically studied C12A7 crystals doped with all kinds of RE of a fixed concentration (1%) first, 23) and then detailed investigations of Pr- 24) and Tb-doped 25) C12A7 were carried out for radiation detection. In addition, Dy:C12A7 also showed interesting properties in PL and RL, so in this study we synthesized C12A7 single crystals with various Dy concentrations and investigated the detailed properties.…”