Multiband Orange-Red Luminescence of Eu3+ Ions Based on the Pyrochlore-Structured Host Crystal

Pyrochlore-type yttrium stannate (Y 2 Sn 2 O 7 ) doped with trivalent europium ions (Eu 3+ ) 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 - x Eu x ) 2 Sn 2 O 7 ( 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 5 D 0 → 7 F 1 and electric−dipole 5 D 0 → 7 F 2 transitions. Inhomogeneous broadening possibly arising from the site-to-site variation of Eu 3+ 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.