KMnF3:Yb3+,Er3+@KMnF3:Yb3+ active-core–active-shell nanoparticles with enhanced red up-conversion fluorescence for polymer-based waveguide amplifiers operating at 650 nm

Abstract

We demonstrated optical amplification at 650 nm in KMnF₃:Yb³⁺,Er³⁺@KMnF₃:Yb³⁺ active-core–active-shell nanoparticle (NP) doped polymer waveguides pumped by a 976 nm laser diode for the first time. KMnF₃:Yb³⁺,Er³⁺ NPs were synthesized via a solvothermal method. With the excitation of a 976 nm laser diode, bright red upconversion (UC) fluorescence was observed from KMnF₃:Yb³⁺,Er³⁺ NPs owing to the existence of efficient energy transfer between Er³⁺ and Mn²⁺:²H_11/2,⁴S_3/2 + ⁶A₁ → ⁴I_15/2 + ⁴T₁,²H_9/2 + ⁶A₁ → ⁴I_13/2 + ⁴T₁ and ⁴I_15/2 + ⁴T₁ → ⁴F_9/2 + ⁶A₁. The red UC emissions originated from the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺. Furthermore, the red UC emissions of KMnF₃:18 mol% Yb³⁺,1 mol% Er³⁺@KMnF₃:2 mol% Yb³⁺ NPs were enhanced by 7.5 times compared to that of KMnF₃:18 mol% Yb³⁺,1 mol% Er³⁺ core-only NPs after coating an active shell containing Yb³⁺ ions on the core-only NPs. The above results showed that the active-shell could be used to not only suppress surface quenching but also transfer the pump light to the core region efficiently through Yb³⁺ ions inside the active-shell. By using KMnF₃:18 mol% Yb³⁺,1 mol% Er³⁺@KMnF₃:2 mol% Yb³⁺ NPs as the gain medium and doping NPs into a polymer waveguide, we constructed polymer-based waveguide amplifiers. For an input signal power of 7.4 mW and a pump power of 45.2 mW, a relative optical gain of ∼3.5 dB was obtained at 650 nm in a 17 mm-long waveguide.