Photoluminescent and electroluminescent characteristics of various Bi-activated niobate-based oxide phosphor thin films

Abstract

The photoluminescent (PL) and electroluminescent (EL) characteristics in the thin films of various Bi-activated niobate-based oxide phosphors have been investigated. LaNbO 4:Bi, GdNbO 4:Bi and YNbO 4:Bi phosphor thin films were prepared on thick BaTiO 3 ceramic sheet substrates by either a conventional or a combinatorial radio frequency magnetron sputtering deposition followed by postannealing at a high temperature. Blue PL emissions were observed from Bi-activated niobate-based oxide phosphor thin films postannealed at a temperature above approximately 800 °C in air or a pure Ar gas atmosphere. The excitation spectra of the blue PL emissions as well as the blue emission spectra observed from LaNbO 4:Bi, GdNbO 4:Bi and YNbO 4:Bi phosphor thin films exhibited an increasing red-shift in that order. In addition, blue, whitish blue-green or blue-green emissions were observed from thin-film electroluminescent devices fabricated with a LaNbO 4:Bi, a GdNbO 4:Bi or a YNbO 4:Bi thin-film emitting layer, respectively. However, the EL emission spectra observed from these TFEL devices exhibited a red-shift relative to the PL emission spectra observed from the respective phosphor thin films. The resulting difference between the observed PL and EL emission spectra may be explained by the 6 s 2–6 s6p transitions in Bi 3+ ions. In particular, the long-wavelength bands observed in the EL emissions may be attributable to the selection rule resolved by a high electric field applied to the phosphor thin films.