Cross-relaxation induced tunable emissions from the Tm³⁺/Er ³⁺/Eu³⁺ ions activated BaGd₂O₄ nanoneedles

Tm³⁺, Er³⁺, Tm³⁺/Er³⁺, Tm ³⁺/Er³⁺/Eu³⁺ single, double and triple activator ion/ions doped nanocrystalline BaGd₂O₄ (BG) phosphors were prepared by a Pechini type sol-gel process. After annealing at 1300 °C, X-ray diffraction patterns confirmed their orthorhombic structure. Field-emission transmission electron microscope images of the BG sample indicated a nanoneedle-type morphology. Photoluminescence (PL) and cathodoluminescence (CL) measurements were utilized to establish the emission properties of rare-earth ions doped nanocrystalline BG host lattice. Under near-ultraviolet (NUV) excitations, BG:Tm³⁺ and BG:Er³⁺ exhibited their characteristic emissions in the blue and green regions, respectively, while BG:Tm³⁺/Er³⁺ and BG:Tm ³⁺/Er³⁺/Eu³⁺ showed cyan and white light emissions, respectively, when doped with appropriate amounts of activator ions. In the PL, the cross-relaxation process is dominant rather than the energy transfer process. Due to the different mechanism from PL, the CL spectra showed different emission features of BG:Tm³⁺/Er³⁺/Eu ³⁺ phosphor. The CL spectra of BG:Tm³⁺ and BG:Er ³⁺ established the high purity blue and green emissions, respectively. From the PL and CL investigations, the white-light emission was realized from the single-phase BG:Tm³⁺/Er³⁺/Eu ³⁺ phosphor under NUV and low voltage electron beam excitations.