Scintillation and photoluminescence properties of (Tl_1−xA_x)MgCl₃ (where A = alkali metal)

We developed (Tl_1−x A_x)MgCl₃ (A = Li, Na, K, Rb, and Cs) crystalline scintillators to improve by cation substitution the scintillation properties of TlMgCl₃, for which we have previously reported good scintillation properties (light yield = 46,000 photons/MeV and scintillation decay time constants = 60 ns (∼25%) and 350 ns (∼75%)). The X-ray-induced scintillation spectra of these (Tl_1−x A_x)MgCl₃ scintillators exhibited an intense emission band at 420 nm, which corresponds to the wavelength observed for TlMgCl₃. This means that the light-emitting mechanisms of (Tl_1−xA_x)MgCl₃ are similar to that in TlMgCl₃. The light yields of (Tl_0.995K_0.005)MgCl₃ (55,000 photons/MeV) and (Tl_0.995Cs_0.005)MgCl₃ (49,000 photons/MeV) were higher than that of TlMgCl₃ (46,000 photons/MeV). This is attributed to the increased number of electron–hole pairs contributing to the scintillation owing to the decreased number of trapped electrons and holes, as revealed by the lower intensity of thermoluminescence. As a result, we succeeded in increasing the light yields by cation substitution.