Photon cascade emission of image ion in alkaline-earth fluorides

Absorption, emission, excitation spectra of image, image, image crystals doped by image in concentration ranging from 0.005% to few molar % were studied in 1.4–10 eV spectral region. Specific type of Pr centres possessing photon cascade emission (PCE active) was observed in all crystals. Concentration of centres monitored by excitation and emission spectra grows superlinearly with increasing of Pr concentration in image and image crystals. A new additional absorption band at 7.0 eV which coincided with excitation band of PCE-active centres was observed in image crystals. The absorption coefficient of this band grows twice that coefficient of 5.7 eV band of single Pr centres.