Yb3+-sensitized visibleNi2+photon upconversion in codopedCsCdBr3andCsMgBr3

Abstract

Near-infrared excitation of ${\mathrm{Yb}}^{3+}\phantom{\rule{0.2em}{0ex}}^{2}F_{7∕2}\ensuremath{\rightarrow}^{2}F_{5∕2}$ at $10\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the linear chain $\mathrm{Cs}\mathrm{M}{\mathrm{Br}}_{3}:{\mathrm{Ni}}^{2+},{\mathrm{Yb}}^{3+}\phantom{\rule{0.2em}{0ex}}(M=\mathrm{Cd},\mathrm{Mg})$ structure leads to green luminescence from ${\mathrm{Yb}}^{3+}$ pairs and red ${\mathrm{Ni}}^{2+}$ upconversion luminescence at cryogenic temperatures. The broad red upconversion luminescence is assigned to the $^{1}T_{2g}\ensuremath{\rightarrow}^{3}A_{2g}$ transition of ${\mathrm{Ni}}^{2+}$. The upconversion excitation spectrum indicates that the active mechanism in these systems involves both ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Ni}}^{2+}$ ions. Lifetime and power dependence data allow one to identify a ground-state-absorption (GSA) energy-transfer upconversion (ETU) as the underlying upconversion mechanism for the ${\mathrm{Yb}}^{3+}\text{\ensuremath{-}}{\mathrm{Ni}}^{2+}$ system in doubly doped $\mathrm{Cs}\mathrm{Cd}{\mathrm{Br}}_{3}$ and $\mathrm{Cs}\mathrm{Mg}{\mathrm{Br}}_{3}$. A less efficient single-ion GSA excited-state-absorption (ESA) process within ${\mathrm{Ni}}^{2+}$ is also observed in the title compounds. However, whereas the GSA/ESA process requires an excitation energy above $11\phantom{\rule{0.2em}{0ex}}200\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, it is possible to sensitize the ${\mathrm{Ni}}^{2+}$ upconversion via ${\mathrm{Yb}}^{3+}$ excitation at energies around $10\phantom{\rule{0.2em}{0ex}}200\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and around $10\phantom{\rule{0.2em}{0ex}}600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in $\mathrm{Cs}\mathrm{Cd}{\mathrm{Br}}_{3}$ and $\mathrm{Cs}\mathrm{Mg}{\mathrm{Br}}_{3}$. It is shown that only those ${\mathrm{Ni}}^{2+}$ ions neighboring to ${\mathrm{Yb}}^{3+}$ ions are relevant for the upconversion induced by ${\mathrm{Yb}}^{3+}$ excitation.