Sensitized high-order ultraviolet upconversion emissions of Gd3+ by Er3+ in NaYF4 microcrystals

High-order ultraviolet (UV) upconversion (UC) emissions of Gd3+ and Er3+ ions were observed in NaYF4:Yb3+/Gd3+/Er3+ microcrystals under 980 nm excitation. These UC emissions came from six- and five-photon UC processes at low pump power range, which were confirmed by the pumping power dependences of UC fluorescence intensities. In these high-order UC processes, energy transfer (ET) processes of Er3+ → Gd3+ played crucial roles in populating the excited states of Gd3+ ions. Experiments on concentration variation and dynamic analysis revealed the ET processes between Er3+ and Gd3+ in detail. Some of possible population routes for populating excited Gd3+ ions were proposed based on spectral and dynamic analysis.

Under 980 nm excitation, ultraviolet (UV) upconversion (UC) emissions of Gd3+ and Er3+ were observed in NaYF4:Yb3+/Gd3+/Er3+ microcrystals. In the complex frequency UC processes, ETs from Er3+ to Gd3+ play crucial roles in populating the excited Gd3+ and producing the high-order UV UC emissions of Gd3+. Experiments on concentration variation revealed the ET processes between Er3+ and Gd3+ in detail.Figure optionsDownload as PowerPoint slideHighlights
► Under 980 nm excitation, Yb3+/Gd3+/Er3+ codoped NaYF4 microcrystals emitted UV UC fluorescence and presented the characteristic emissions of Gd3+ and Er3+ ions.
► Power dependence analysis confirmed that these UC emissions came from five- and six-photon processes in low power region.
► Experiments on concentration variation demonstrated the ET processes from Er3+ to Gd3+ ions.
► Experiments on spectral and dynamic analysis confirmed some of ET routes between Er3+ and Gd3+.