The optical properties and scintillation mechanism in pure and ${\mathrm{Ce}}^{3+}$-doped ${\mathrm{K}}_2\mathrm{La}{X}_5$ and $\mathrm{La}{X}_3$ have been determined under x-ray, $\gamma$-ray, vacuum ultraviolet light, and synchrotron radiation excitation. Special attention is paid to the influence of anions $X={\mathrm{Cl}}^{-},$ ${\mathrm{Br}}^{-},$ and ${\mathrm{I}}^{-},$ and a comparison is made with properties of pure and ${\mathrm{Eu}}^{2+}$-doped $\mathrm{K}X$ compounds. The energies of the $5d$ excited states of ${\mathrm{Ce}}^{3+}$ have been determined, and the total crystal field splitting and the centroid shift are discussed. An excitation across the band gap creates a combination of self-trapped exciton (STE) and ${\mathrm{Ce}}^{3+}$ emission. These emissions are often anticorrelated when temperature or ${\mathrm{Ce}}^{3+}$ concentration is changed. Their ratio is related to the STE mobility and STE creation rate. Clear trends in the optical properties and scintillation mechanism are observed along the halide series.

• Received 14 March 2003

DOI:https://doi.org/10.1103/PhysRevB.68.045108