Multiband orange-red luminescence of Eu³⁺ ions based on the pyrochlore-structured host crystal

Pyrochlore-type yttrium stannate (Y₂Sn₂O₇) doped with trivalent europium ions (Eu³⁺) was synthesized as thin films by the sol-gel method. X-ray diffractometry, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy were used to evaluate the crystallinity and purity of the films, which was of prime importance in investigating the optical properties. It was shown that heat treatment of the films at 1000°C was enough to obtain highly crystalline and phase-pure samples. Photoluminescence spectra of the (Y_1-xEu_x) ₂Sn₂O₇ (x = 0.01-0.20) films indicated the simultaneous occurrence of five predominant orange-red band emissions at a single-wavelength ultraviolet excitation due to doubly split magnetic-dipole ⁵Do → ⁷F₁ and electric-dipole ⁵D₀ → ⁷F₂ transitions. Inhomogeneous broadening possibly arising from the site-to-site variation of Eu³⁺ was also observed. These results demonstrate that we have succeeded in synthesizing a single-phase crystalline phosphor material having the chromaticity corresponding to a region between pink and yellowish pink.