Structural and luminescent properties and energy transfer from Tb3+ to Eu3+ in LaVO4:xTb3+/ yEu3+ phosphors

Abstract

The structural and optical properties of Eu3+, Tb3+ doped and Eu3+/Tb3+ codoped LaVO4 a self-activated host have been studied in detail. The XRD patterns of phosphor samples show that the LaVO4 crystallizes in monoclinic phase with the P21/n space group. The average crystallite size is ∼ 60 nm which decreases on doping of Eu3+, Tb3+ ions. The SEM patterns show particles of nearly spherical shape whose average size (∼ 5.64 µm) decrease on doping. The UV-Vis absorption and FTIR spectra of the samples were also studied. The excitation spectra of Eu3+, Tb3+ doped and Eu3+/Tb3+ codoped LaVO4 samples show intense charge transfer band (CTB) at 323 nm due to [VO4]3- group of host material. Eu3+ doped /codoped phosphor samples, also show large number of sharp bands due to Eu3+ ion alongwith CTB. On the other hand, Tb3+ doped LaVO4 show broad band near 375 nm. Photoluminescence could be observed from 5D0, 5D1 to different levels of ground state (7FJ) in Eu3+ in which the 5D0-7F2 at 614 nm is very intense. Similarly, in case of Tb3+, bands could be observed from 5D4-7FJ in which the bands in green and blue at 543, 489 nm due to 5D4-5F5 and 5D4-7F6 transitions respectively are very intense. Thus, samples containing Eu3+/Tb3+ together emit blue, green and red colors on 323 nm excitation. The phosphor samples containing LaVO4:Tb3+/Eu3+ also show energy transfer from Tb3+ to Eu3+ ion on excitation with CTB wavelength. The energy transfer efficiency has also been calculated by considering the changes in emission intensity of 543 nm (5D4-7F5) band and the lifetime of 5D4 level of Tb3+ ion for different concentrations of Eu3+ and fixed concentration of Tb3+ ion in LaVO4:1Tb3+/yEu3+ phosphor samples. The interaction of two ions was found dipole-dipole.