Down-conversion and structural characterizations of trivalent terbium-doped garnet nanocrystalline phosphors for lighting applications

Nanocrystalline green-emitting Tb³⁺-doped Y₃Al₅O₁₂ (garnet) nanophosphors were synthesized via an efficient and economical solution combustion route using hexamethylenetetramine (C₆H₁₂N₄) as a fuel. The samples were synthesized at 500 °C and calcined at 650, 950 and 1050 °C for further analysis. The structural and lattice parameters for both undoped and Tb³⁺-doped Y₃Al₅O₁₂ materials were determined by Rietveld refinement using diffraction data. The pure crystalline phase of YAG:Tb³⁺ having a cubic unit cell with Ia\( \overline{{3\text{d}}} \) space group was obtained at 500 °C without the presence of intermediate phases like YAlO₃ and Y₄Al₂O₉. FTIR analysis proposed the presence of different bands corresponding to AlO₄ tetrahedra and AlO₆ octahedra supporting the XRD measurements. The synthesis of nanocrystalline materials with slightly agglomerated particles with narrow size distribution was confirmed by transmission electron microscope (TEM). Energy dispersive X-ray (EDX) examination confirmed the synthesis of desired samples with the existence of components coordinated inside the crystalline host. The phosphors yielded bright emission in the green region owing to the ⁵D₄ → ⁷F₅ (544 nm) transition at λ_ex = 267 nm. Critical distance affirmed that the transfer of energy happens by means of the multipolar association phenomenon. The down-conversion and structural investigations support the convenient utility of Y₃Al₅O₁₂:Tb³⁺ materials in solid-state lighting and other optoelectronic devices.