Intense White Luminescence from Combustion Synthesized Ca12Al14O33: Yb3+/Yb2+ Single Phase Phosphor

Abstract

The Ca(12)Al(14)O(33):Yb(3+)/Yb(2+) single phase nano-phosphor has been synthesized through combustion route and its luminescence and lifetime studies have been carried out up to 20 K using 976 and 266 nm excitations. The samples heated in open atmosphere have shown the presence of Yb in Yb(3+) and Yb(2+) states. The 976 nm excitation results a cooperative upconversion emission at 486 nm due to the Yb(3+) state and a broad band in the blue region and has been assigned to arise from the defect centers. The 266 nm excitation on the other hand results a broad emission band even from as-synthesized phosphor without doping of Yb, the width of which increases in presence of Yb due to the emission from Yb(2+) ions formed in heated samples. The white emission covers almost whole visible region with bandwidth 190 nm. The ions in Yb(2+) state has been found to increase with the increase in heating temperature up to 1,273 K. A back conversion of Yb(2+) to Yb(3+) has been observed for higher temperatures. Effect of boric and phosphoric acids as flux on the emission properties of Yb(3+) and Yb(2+) states have been examined and discussed. Quantum yield of emission has also been determined for different samples.