Thermal neutron scintillation improvement in Ce:Li₆Y(BO₃)₃ single crystals by thermal treatment

Abstract

Efficient, low-cost, and stable solid-state materials for portable thermal neutron detection are highly expected in order to substitute the currently used 3He and BF3 tank detectors. Li-glasses and halide compounds have emerged as candidates, however, they present critical drawbacks for practical implementations. Ce:Li6Y(BO3)3 is a promising oxide candidate that however has been disregarded due to its negligibly low light yield, caused by a poor crystalline and optical quality. In this study, we demonstrate that a post-growth thermal treatment is the key parameter to drastically reduce the concentration of intrinsic defects and scattering centers that lead to severe non-radiative recombination. Even though this annealing also involves the oxidation of activator Ce3+ ions to Ce4+, a drastic enhancement of the light yield by ~600% is achieved independently of the Ce3+ concentration within the considered range. The light yield of 4650 ph/n is already close to that of commercial GS20 with 6000 ph/n.

Scattering-free Ce:LYBO single crystals for thermal neutron detection

“…In a precedent publication, it was shown that the scintillation properties of LYBO can be drastically improved after air annealing close to the T m of LYBO. 11) Though this treatment causes a remarkable reduction in the concentration of scattering centers in LYBO, the latter do not represent the main source of non-radiative recombination, as will be seen later in the case of scattering-free crystals. In order to visualize the remaining scattering after annealing, a He-Ne laser with a five times higher power than a laser pointer was used.…”

“…Ce-doped Li 6 Y(BO 3 ) 3 (LYBO) stands out as a promising alternative. 10,11) Compared with other candidates, it compromises a priori of all required basic material properties: a high Li content (3.06 × 10 22 cm -3 ), good chemical stability, a trivalent site (Y 3+ ) for efficient Ce 3+ doping, cheap and abundant constituents, and the possibility to grow large single crystals for low-cost mass production. Despite these promising characteristics, the poor crystalline and optical quality of Ce:LYBO crystals has largely discouraged its development for scintillation applications so far.…”

“…[12][13][14][15][16] Recently, we have demonstrated that a post-growth thermal treatment close to T m can drastically reduce the milky appearance of crystals while the light yield (LY) rises to 4650 ph/n. 11) Nevertheless, to date it is still unknown, on the one hand, what are the origin and nature of the scattering centers, and on the other hand, what is the annealing mechanism that improves the scintillation response.…”

“…Scattering centers in as-grown Ce:LYBO crystals can be easily visualized with laser pointers, for example, the light of a green one (550 nm, 1 mW) exhibits a strong scattering path even in slightly milky crystals as shown in our recent work. 11) To investigate the nature of these scattering centers, the microstructure of fine-polished b-plane LYBO crystals was investigated by FE-SEM and AFM, as shown in Figs. 1(a) and 1(b), respectively.…”

“…In analogy with previous findings on scattering Ce:LYBO crystals, scattering-free ones need to be annealed under air to measure their scintillation performance. 11) The remarkable decrease in non-radiative recombination centers after annealing is attributed to a reduction in oxygen vacancies present in as-grown crystals. This hypothesis is further supported by the enhanced transmittance close to the absorption cutoff (see Fig.…”