MODULATION OF PHOTOLUMINESCENT INTENSITY BY APPLYING HIGH ELECTRIC-FIELD IN DOUBLY INSULATED CAS-EU PHOSPHOR THIN-FILMS

Emission modulation effect produced by applying electric fields in a CaS:Eu phosphor thin film was studied. The CaS:Eu polycrystalline thin film was sandwiched between the insulating layers so that high electric fields up to 10(6) V/cm could be applied to the film. As a result, the photoluminescent intensity decreased with increasing applied electric field and the maximum modulation degree of 97% was obtained. The photoluminescent modulation effect was found to be caused by field-induced ionization (a kind of tunneling effect) of the excited state of Eu2+ localized-luminescent centers. These results indicated that the photoluminescent intensity of the phosphor thin films can be modulated by the electric field as well as by excitation intensity. These new features should offer the phosphor thin films new applications such as a spatial light modulator.