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

The benefits of doping CsEuBr and CsEuI with Sm are studied for near-infrared scintillator applications. It is shown that undoped CsEuI suffers from a high probability of self-absorption, which is almost completely absent in CsEuI:2% Sm. Sm doping is also used to gain insight in the migration rate of Eu excitations in CsEuBr and CsEuI, 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 excitation and emission spectra which were studied between 10 K and 300 K. The scintillation characteristics of CsEuI:2% Sm is compared to that of the undoped samples. An improvement of energy resolution from 11% to 7.5% is found upon doping CsEuI 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.