Comparative investigation on upconversion luminescence properties of Lu${}_2$O${}_3$:Er/Yb and Lu${}_2$O${}_2$S:Er/Yb phosphors

A series of (Lu${}_{0.99-x}$Er${}_{0.01}$Yb${}_x$)${}_2$O${}_3$ and (Lu${}_{0.99-x}$Er${}_{0.01}$Yb${}_x$)${}_2$O${}_2$S (x = 0 - 0.1) phosphor particles are prepared to investigate their upconversion luminescence properties. Under 980 nm pumping laser, the two phosphors both exhibit strong green emission at ≈ 520 - 573 nm and weak red emission at ≈ 648 - 688 nm arising from ${}^4$S${}_{3/2}$/${}^2$H${}_{11/2}$ → ${}^4$I${}_{15/2}$ and ${}^4$F${}_{9/2}$ → ${}^4$I${}_{15/2}$ transitions of Er${}^{3+}$, respectively. The optimum concentrations of Yb${}^{3+}$ sensitizers are found to be 1.0 at% in oxide and 0.5 at% in oxysulfide, and their corresponding CIE chromaticity coordinates are (0.29, 0.69) and (0.33, 0.65). The Lu${}_2$O${}_2$S:Er/Yb phosphor exhibits ≈42 times higher luminescence intensity than the Lu${}_2$O${}_3$:Er/Yb contrast. More Yb${}^{3+}$ addition further increases the proportion of red emission by the cross-relaxation between adjacent Yb${}^{3+}$ and Er${}^{3+}$ and the multiphonon relaxation. The luminescence intensities of the two phosphors gradually increase as the laser output power increases and the upconversion mechanisms are both identified to be two-phonon processes. The Lu${}_2$O${}_2$S:Er/Yb phosphor has a shorter lifetime than the Lu${}_2$O${}_3$:Er/Yb counterpart, whereas the lifetime for the red emission is longer than that for the green emission in each case. (© 2021 Wiley‐VCH GmbH)