Wei-Lun Wei

The emission of a luminescent material is governed not only by the centers it contains but by how they are excited, a distinction that becomes decisive when several emitting phases coexist. Eu- and Dy-doped strontium aluminates, the most widely used persistent-luminescence phosphors, are frequently multiphase, which complicates the assignment of their emission. Here, a mixed-phase Eu,Dy-doped strontium aluminate ceramic, with estimated phase fractions of 71.4% SrAl2O4 and 28.6% Sr4Al14O25 from powder X-ray diffraction, is characterized at the Taiwan Photon Source 23A hard X-ray nanoprobe by X-ray-excited optical luminescence (XEOL) spectroscopy and mapping, X-ray fluorescence (XRF) mapping, and X-ray absorption spectroscopy (XAS). The dominant spectral contributions depend on the excitation channel: under 9670 eV excitation the XEOL is dominated by a 493 nm Eu2+ band characteristic of the minority Sr4Al14O25 phase, whereas ultraviolet (UV)-excited photoluminescence (PL) is dominated by the 519 nm band characteristic of the majority SrAl2O4 host. Because broadband hard X-ray excitation is less site-selective than direct UV excitation, XEOL additionally reveals Eu3+ and Dy3+ lines scarcely visible in PL and sharp Cr3+-related emission near 692–694 nm, and XAS supports these oxidation-state assignments. Energy-dispersive XRF detected trace Mn, whose K-edge absorption profile was most consistent with Mn2+, although no Mn2+ emission was resolved. A weak violet band near 408 nm is tentatively assigned to an F-type color center, although a second-site Eu2+ contribution cannot be excluded. This approach resolves multiple emission features in a multiphase phosphor and demonstrates excitation-dependent spectral weighting consistent with different phase contributions.

Two-dimensional (2D) (OLM)₂Cs_n−1Pb_nBr_3n+1 perovskite nanoplates with n = 2 and 3 exhibit bright and tunable violet-to-blue photoluminescence, offering composition-dependent optical properties.

Pulsed-laser deposition was utilized to fabricate Eu-doped ZnO epitaxial films on c-plane sapphire substrates with Eu concentrations ranging from 0.5 to 4.0 at. %. The structural properties were analyzed using x-ray diffraction surface normal radial scans and azimuthal cone scans, which confirmed the epitaxy of the film samples. Reciprocal space mapping was performed on ZnO(101̄1) to visualize the effect of Eu incorporation. X-ray fluorescence mapping confirmed the homogeneous distribution of Zn and Eu, and x-ray absorption near-edge structure spectra directly confirmed the trivalent state of Eu ions. The optical properties were assessed using temperature-dependent photoluminescence (PL). Various defects were identified. With increasing Eu dopant concentration, PL emissions from defects and the Eu 4f-intraband transitions gradually became the predominant features in the PL spectra at low temperatures. Furthermore, PL analysis suggested that Eu ions substituted Zn, occupying sites with lower C3v symmetry due to the distortion caused by Eu incorporation.