Rare earth doped lithium titanate (Li2TiO3) for potential phosphor applications

Lithium titanate ceramics doped with three rare earth (RE) ions namely Eu3+, Dy3+ and Tb3+ were synthesized and their photoluminescence (PL) properties were investigated. PL spectra of Eu doped sample showed peaks corresponding to the 5D0→7Fj (j=0, 1, 2, 3 and 4) transitions under 230 nm excitation. Strong red emission coming from the hypersensitive 5D0→7F2 transition of Eu3+ ion suggested the presence of the dopant ion in a highly asymmetric environment. Dy doped samples showed the Dy3+ emission characteristic due to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions. Their relative intensity ratios also suggested the presence of asymmetric environment around the metal ion. In case of the Tb3+ doped sample blue-green emission corresponding to the 5D4→7Fj (j=6, 5 and 4) transitions was seen. The fluorescence lifetimes of Eu3+, Dy3+ and Tb3+ ions were found to be 645, 900 and 740 μs, respectively. PL intensity of the individual rare earth doped samples was compared with commercial red and green phosphors. It was found that the emission from Eu doped titanate sample was 46% of the commercial red phosphor and in case of the Tb samples it was 30% when excited at 230 nm. However, the synthesized Eu doped titanate sample showed better color purity as compared to the commercial phosphor. The titanate host was doped with all the three rare earths to get white light emission from the system. The individual rare earth ion content was optimized so as to get a near white light emission. The color coordinates of the triple doped systems were evaluated and plotted on the CIE x-y diagram. Our results suggest that lithium titanate has enough potential to be a phosphor material.