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Tm3+/Er3+/Eu3+/Er3+, Tm3+/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:Tm3+/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+/Eu3+ phosphor. The CL spectra of BG:Tm3+ and BG:Er3+ 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+/Eu3+ phosphor under NUV and low voltage electron beam excitations. [ABSTRACT FROM AUTHOR]