Temporal dynamics of upconversion luminescence in Er³⁺, Yb³⁺ co-doped crystalline KY(WO₄)₂ thin films

Crystalline $Er^{3+}$ and $Yb^{3+}$ singly and doubly doped $KY(WO_4)_2$ thin films were grown by low-temperature liquid-phase epitaxy. Absorption, luminescence, excitation and temporal evolution measurements were carried out for both $Er^{3+}$ and $Yb^{3+}$ transitions from 10K to room temperature. Green $Er^{3+}$ upconversion luminescence was observed after $Yb^{3+}$ and $Er^{3+}$ excitation. The mechanisms responsible for the upconversion phenomena detected in each case were identified.