Influence of flux and Ho$^{3+}$ doping concentration on upconversion luminescent performance of BaGd$_2$ZnO$_5$ : Er$^{3+}$/Yb$^{3+}$ phosphors under 980 nm laser excitation

Utilizing the conventional high-temperature solid-phase method, two sets of BaGd$_2$ZnO$_5$ phosphors were synthesized with fixed Er$^{3+}$/Yb$^{3+}$ concentrations while varying the flux and Ho$^{3+}$ concentrations. XRD results confirmed that the obtained products were all pure-phase BaGd$_2$ZnO$_5$, with no alterations in crystal phases observed with varying levels of Ho$^{3+}$ doping and different flux agents. Employing 980 nm as the excitation source, upconversion emission spectra of the samples were recorded under identical conditions. The relationship between the upconversion luminescence intensity of the Ho$^{3+}$-doped samples and the laser working current was investigated. Analysis using the intensity-constraining formula revealed that both red and green upconversion emissions in the samples were two-photon processes. Additionally, the energy transfer processes involved were explored. The temperature effect on the Er$^{3+}$/Yb$^{3+}$/Ho$^{3+}$ tri-doped samples was also examined, and the activation energy of the samples was calculated.