Phosphorescence Mechanism in CdF2:Eu3+

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Abstract
Single crystals of CdF2, doped with Eu3+, were grown by the Bridgman method, and shown by fluorescence and absorption spectra to contain no detectable Eu2+, irrespective of the presence of Na+ or Y3+ as added impurities. Ultraviolet irradiation at 77°K produced a new broad absorption band near 3400 Å, which disappeared on warming, with associated thermoluminescence. A complex ESR signal associated with this band is attributed to Eu2+, formed during the irradiation. A mechanism proposed for the luminescence processes involves formation of Eu2+ in the excitation and trapping steps, with the luminescence of Eu3+ resulting from a resonance transfer of excitation energy from the recombination site.