Avoiding concentration quenching and self-absorption in Cs 4 EuX 6 (X = Br, I) by Sm 2+ doping.

The benefits of doping Cs 4 EuBr 6 and Cs 4 EuI 6 with Sm 2+ are studied for near-infrared scintillator applications. It is shown that undoped Cs 4 EuI 6 suffers from a high probability of self-absorption, which is almost completely absent in Cs 4 EuI 6 :2% Sm. Sm 2+ doping is also used to gain insight in the migration rate of Eu 2+ excitations in Cs 4 EuBr 6 and Cs 4 EuI 6 , which shows that concentration quenching is weak, but still significant in the undoped compounds. Both self-absorption and concentration quenching are linked to the spectral overlap of the Eu 2+ excitation and emission spectra which were studied between 10 K and 300 K. The scintillation characteristics of Cs 4 EuI 6 :2% Sm is compared to that of the undoped samples. An improvement of energy resolution from 11% to 7.5% is found upon doping Cs 4 EuI 6 with 2% Sm and the scintillation decay time shortens from 4.8 s to 3.5 s in samples of around 3 mm in size.