Ceramics-Silikáty 56 (4) 295-300 (2012)

EFFECT OF ALKALINE IONS ON THE PHASE EVOLUTION, PHOTOLUMINESCENCE, AND AFTERGLOW PROPERTIES OF SrAl₂O₄: Eu²⁺, Dy³⁺ PHOSPHOR

H. Shin, S. Ullah, K. Chung

A series of SrAl₂O₄: Eu²⁺, Dy³⁺ long-afterglow (LAG) phosphors with varying concentration of Li⁺, Na⁺ and K⁺, has been synthesized. The increased concentration of the three types of alkaline ions does not decrease the quantity of the total luminescent phases (SrAl₂O₄ plus Sr₄Al₁₄O₂₅), but a different set of secondary phases has been evoluted for the K⁺-added series due to the failure of the incorporation of relatively large K⁺ (1.38 Å) to the Sr²⁺ (1.18 Å) site in the hosts, unlike the cases of smaller Li⁺ (0.76 Å) and Na⁺ (1.02 Å) ions. PL excitation, PL emission, and LAG luminescence, are decreased by all investigated alkaline ions, which would be due to the diminished incorporation of Eu²⁺ and Dy³⁺ activators into the luminescent hosts by the alkaline ions. For the cases of the Li⁺ and Na^+-added series, the incorporated Li⁺ or Na⁺ to the luminescent hosts would also limit the activation of Eu²⁺ and charge trapping/detrapping of Dy³⁺ to yield the diminished PL properties and LAG luminescence. The type of defect complex formed by the addition of Li⁺ and Na⁺ ions has been deduced and compared with that formed when no alkaline ion is added.

Keywords: SrAl₂O₄, Afterglow, Phosphor, Alkaline ions, Defect complex