A blue to green tunable Ba3GdP3O12:Tb3+ nanophosphor: structural and opto-electronic analysis

A series of blue–green Ba₃Gd_(1−x)P₃O₁₂: xTb³⁺ nanocrystals has been successfully prepared via the urea-assisted solution-combustion method. Its structure, morphology, energy-transfer mechanism, photoluminescent (PL) excitation-emission and decay time behavior were investigated in detail employing powder X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Diffuse Reflectance (DR) and PL spectroscopy. The Rietveld analysis exposed the cubic phase of all the nanophosphors with I-43d (220) space group and infers that Gd³⁺ ions can be well substituted by Tb³⁺ ions without any major alteration in the crystal prototype of the host lattice. The optical band-gap of the host was calculated to be 4.9 eV, unveiling the high potential as a host for lanthanide activators. Under the excitation at λ_ex = 224 nm, the photoluminescent emission spectra exhibited the two main characteristic peaks at 545 nm and 487 nm as a result of ⁵D₄ → ⁷F₅ (green and magnetic-dipole) and ⁵D₄ → ⁷F₆ (blue and electric-dipole) transitions, respectively. The decay analysis showed that the activator occupies a single crystallographic site, a fact that is also supported by the Rietveld refinement. The critical distance of the energy transfer (19.87 Å) integrated with Dexter’s modeling inferred about the energy migration (dipole–dipole). The PL result showed that the blue-to-green tunable emission can be achieved simply via varying the dopant concentration, with 7 mol% as the optimum concentration for standard CIE coordinates of green emission. All the results suggest that Ba₃Gd_(1−x)P₃O₁₂: xTb³⁺ crystals may find their use as a green phosphor component in display devices and solid-state lighting.