UV–visible–NIR spectroscopy was performed by diffuse reflectance with integrating sphere (Perkin Elmer l35) in
the 300–1100 nm range, step 0.3 nm, using BaSO4 as a reference. The positions of the main absorbance peaks in
the optical spectra were determined through a deconvolution procedure (PFM, OriginLab), that allowed to obtain
averaged values of CF strength (Dqcub), peak splitting (d), crystal field stabilization energy (CFSE), Racah B35
parameter and nephelauxetic ratio b35 (i.e. B35=B0, where B35 is experimental and B0 is the value of the free ion [20]).
Dq was estimated by the Tanabe–Sugano diagrams and fitting spin-allowed transitions; B35 was calculated by spinallowed
transitions [20–22]; d was measured as FWHM on some peaks of optical spectra; the CFSE was calculated by
Dq values [11].