GROWTH AND CHARACTERISTICS OF LONG PERSISTENT SRAL2O4-BASED AND CAAL2O4-BASED PHOSPHOR CRYSTALS BY A FLOATING-ZONE TECHNIQUE

Long persistent phosphor crystals, SrAl2O4 doped with Eu and Dy, and C aAl2O4 doped with Eu and Nd have been grown by a floating zone techniq ue. The intensities and the persistent times of the phosphorescences a re found to depend on the growth atmosphere. SrAl2O4 crystals grown un der H-2-Ar atmosphere and CaAl2O4 crystals grown under Ar atmosphere e xhibit strong and long persistent green and blue phosphorescences peak ing at lambda = 520 and 450 nm, respectively. The spectra of the phosp horescence from the crystals are quite similar to those obtained with sintered powders used for luminous pigments. The persistent time of th e phosphorescence from CaAl2O4 crystals is similar to that obtained wi th sintered powders, while in SrAl2O4 crystals, it is shorter than in sintered powders. The difference in the persistent time is found to be due to Dy and/or Nd dopant concentration added as auxiliary activator s. In SrAl2O4, the Dy concentration in the crystal is about 1/100 of t he sintered powders. The Dy3+ ion is responsible to the persistent tim e of the phosphorescence. (C) 1998 Elsevier Science B.V. All rights re served.