Long-wave UVA radiation excited warm white-light emitting NaGdTiO4: Tm3+/Dy3+/Eu3+ ions tri-doped phosphors: Synthesis, energy transfer and color tunable properties

• The pebble shaped NaGdTiO4 particles were prepared by solid-state reaction method.
• Tm3+ and Dy3+ single doping gives respective blue and cool white light emission.
• The Tm3+/Dy3+ ions co-doped samples give CIE values near to standard white light.
• Addition of Eu3+ ions shifts the CIE values towards warm white light region.
• This single phase white light emitting phosphors have lower CCT values (<5000 K).

NaGdTiO4 (NGT) phosphors doped with different activator ions (Tm3+, Dy3+, and Eu3+) were synthesized by a conventional solid-state reaction method in an ambient atmosphere. These phosphors were characterized by scanning electron microscope images, transmission electron microscope images, X-ray diffraction patterns, Fourier transform infrared spectra, and photoluminescence spectra. All the samples were crystallized in an orthorhombic phase with a space group of Pbcm (57). In Tm3+/Dy3+ ions co-doped samples, white-light emission was observed under near-ultraviolet (NUV) excitation. In addition, the energy transfer between Tm3+ and Dy3+ ions was proved to be a resonant type via an electric dipole–dipole mechanism and the critical distance of energy transfer was calculated to be 19.91 Å. Furthermore, Tm3+/Dy3+/Eu3+ ions tri-doped NGT phosphors demonstrated warm white-light emission by appropriately tuning the activator content, based on the principle of energy transfer. These NUV wavelength excitable phosphors exhibit great potential as a single-phase full-color emitting phosphor for white light-emitting diode applications.

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