NaNbO₃:Pr³⁺: a new red phosphor showing persistent luminescence

Abstract

The Pr(3+)-doped NaNbO(3) perovskite is introduced as a new red phosphor excitable in the near UV region at around 350 nm. A bright single red emission is observed at room temperature and ascribed to transitions between the (1)D(2) excited state and the ground state (3)H(4) of Pr(3+) ions. This peculiar behavior is related to the presence of a low-lying intervalence charge transfer state that contributes to quench the emission from the otherwise emitting (3)P(0) level. Red afterglow is also evidenced in NaNbO(3):Pr(3+). A preliminary model is discussed to clarify the afterglow mechanism.

Effects of doping and epitaxy on optical behavior of NaNbO3 films

“…[24][25][26] The obtained spectrum of PL emission contains a strong narrow line at approximately 2 eV (wavelength 610 nm) in the Pr-doped film ( Figure 5(a)), closely resembling that at 620 nm in the Pr-doped NNO crystal. 9 Thus, also similar to the crystal, the red PL in the film can be ascribed to radiative transitions between the 1 D 2 excited state and the 3 H 4 ground state of Pr 3þ ions. 9 The PL excitation is generally explained by the presence of an intervalence charge transfer state (IVCT) inside the bandgap.…”

“…9 Thus, also similar to the crystal, the red PL in the film can be ascribed to radiative transitions between the 1 D 2 excited state and the 3 H 4 ground state of Pr 3þ ions. 9 The PL excitation is generally explained by the presence of an intervalence charge transfer state (IVCT) inside the bandgap. The existence of this state is indicated by a broad excitation spectrum centered at $3.6 eV (344 nm) in the Pr-doped NNO crystal.…”

“…The existence of this state is indicated by a broad excitation spectrum centered at $3.6 eV (344 nm) in the Pr-doped NNO crystal. 9 The excitation spectrum of the red PL in the Pr-doped NNO film differs significantly from that in the crystal ( Figure 5(b)). A closer inspection reveals a main excitation band centered at $4.4 eV and a weaker one at $3.8 eV in the film.…”

“…[6][7][8] Moreover, the red-color photoluminescence (PL) can be excited by ultraviolet radiation in the Pr-doped NNO crystals and (K,Na)NbO 3 ceramics. [9][10][11] Bulk NNO possesses an orthorhombic crystal structure and exhibits an antiferroelectric behavior at room temperature. 12,13 When epitaxial NNO films are grown on top of cubic substrates, a monoclinic-type ferroelectric r-phase is expected to form in the films.…”

“…Since the Na þ and Pr 3þ ions have very similar ionic radii, it is accepted that Pr 3þ substitutes Na þ in NNO. 9 An excess charge created at Na-site upon Pr-doping can lead to the increased unit-cell volume in the Pr-doped film. The revealed cube-on-cube-type epitaxy of NNO on LSAT suggests that the NNO films exhibit the theoretically predicted r-state, where the ferroelectric polarization has non-zero components along all three crystal directions of the perovskite NNO sub-cell.…”