Effect of Coordination Environment on Luminescence of Crystalline Cerium Halides

The effect of the coordination environment on the photoluminescence of crystalline cerium trihalides CeL₃ (L = F, Cl, Br, I) was investigated. It was found that in the series of anions F_– > Cl_– > Br_– > I_– a bathochromic shift of luminescence maxima is observed, which is correlated with an increase in the degree of Ce–L bond covalency and anion polarisability. Using PBE/3ζ density functional theory and classical Pauling’s approach, calculations of anion polarisability and Ce–L bonding parameters were carried out, revealing a direct correlation between these values and the long-wavelength shift of maxima. This fact allows us to postulate that the bathochromic shift of maxima in the photoluminescence and photoluminescence excitation spectra of solid CeL₃ is due to the nepheloxetic effect, namely, an increase in the degree of covalency of the Ce–L bond, leading to a decrease in the energy gap between the valence zone (np-levels of L_–) and the conduction zone (5d-levels of Ce₃₊). The results demonstrate the possibility of controlling the spectral characteristics of the luminescence of Ce₃₊ compounds by changing the coordination environment, which is important for the development of new cerium-containing luminophores.

trivalent cerium ion, coordination environment, photoluminescence, nepheloxetic effect