Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals

Abstract

The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu³⁺-doped BaZrO₃ (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange-red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon ⁵D₀ → ⁷F₀ transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu³⁺ concentrations of 0-10.0%. The 2.0% Eu³⁺-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu³⁺ ions occupy the six-coordinated Zr⁴⁺ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties.

Keywords: BaZrO3; EXAFS; defect; europium; luminescence.

Figure 1

(a) XRD patterns, (b) FTIR spectra, (c) Raman spectra, and (d) SEM images of the BZO and BZOE samples.

Figure 2

Normalized XANES spectra of the BZOE samples and standards at the (a) Ba L₃-edge, (b) Zr K-edge, and (c) Eu L₃-edge.

Figure 3

Fourier transformed spectra of the BZOE samples and standards at the (a) Ba L₃ edge, (b) Zr K edge, and (c) Eu L₃ edge. Spectra are shifted vertically for clarity.

Figure 4

(a) Excitation spectra with λ_em = 625 nm, emission spectra under (b) λ_ex = 279 nm and (c) λ_ex = 395 nm of the BZOE samples. (d) Effects of Eu³⁺ doping concentration of the BZOE samples on integrated MDT emission intensity of ⁵D₀ → ⁷F₁ transition.

Figure 5

(a) Emission spectra of the BZOE-2 sample recorded at 77 K and (b) corresponding color coordinate diagram of the BZOE-2 sample under 279 and 395 nm excitations with * indicating the Stark components in (a) and arrows 1 and 2 pointing to the coordinates in (b), respectively. (c) Proposed photophysical processes happening under 279 and 395 nm excitations. (d) Schematic showing site selective excitations under 279 nm and 395 nm for the BZOE submicron crystals.

Figure 6

PL decay profiles of the BZOE-2 sample under excitation wavelengths of (a) 279 nm and (b) 395 nm at three different emission wavelengths of 575, 591, and 612 nm corresponding to ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions, respectively. (c) Effects of Eu³⁺ doping concentration of the BZOE samples on (c) average lifetime with * indicated the studied Eu³⁺ concentration (mol %) and (d) quantum yield (λ_ex = 279 nm and λ_em = 625 nm).