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.