Characterization and energy transfer of Sm3+/Tb3+ co-doped ZnO elaborated by auto-combustion method

Abstract

Zinc oxide undoped and co-doped with (Sm³⁺, Tb³⁺), were successfully obtained through an auto-combustion synthesis process. The optical behaviors of these materials were analyzed to determine the impact of Sm³⁺/Tb³⁺ incorporation. The structural characterization by X-ray diffraction (XRD) revealed that the samples crystallize in a hexagonal wurtzite phase. The Judd-Ofelt analysis was applied to the absorption spectra of Sm³⁺ (4 $f^5$) ions to further investigate their optical properties. This allowed for the determination of the three phenomenological parameters (${\Omega }_2$, ${\Omega }_4$ and ${\Omega }_6$), from which theoretical radiative properties were derived. It was found that the JO parameters follow the order: ${\Omega }_4$ > ${\Omega }_6$ >${\Omega }_2$. Photoluminescence (PL) studies revealed the presence of characteristic transitions of Sm³⁺ ions, with a prominent emission at ⁴G_5/2 → ⁶H_7/2 (600 nm). Energy transfer from Tb³⁺ ions to Sm³⁺ ions was evidenced through PL analysis and the Judd-Ofelt method. An improvement was observed in the values of ${\sigma }_e$ and (${\sigma }_e{\Delta \lambda }_{eff}$), as well as in the measured lifetime (${\tau }_{meas}=1.35ms$) of the ⁴G_5/2 → ⁶H_7/2transition after the addition of Tb³⁺ ions. A noticeable increase in radiative lifetime (${\tau }_{rad}=1.50ms$) was recorded following the addition of Tb³⁺. Enhancement of photoluminescence intensity was also observed for the transitions ⁴G_5/2 → ⁶H_5/2 (562 nm), ⁴G_5/2 → ⁶H_7/2 (600 nm), ⁴G_5/2 → ⁶H_9/2 (650 nm) and ⁴G_5/2 → ⁶H_11/2 (700 nm), along with an improvement in quantum efficiency ($\eta =90\%$) for the ⁴G_5/2 excited state. These findings suggest that Sm³⁺, Tb³⁺ co-doped ZnO could be a promising candidate for applications in color display technologies. The correlated color temperature (CCT) was calculated at 3013 K, supporting its potential use in LED (w-LED) applications.