Bifunctional KZnF3:Er3+/Mn2+ perovskite nanoparticles for achieving pure red upconversion luminescence and magnetic resonance imaging

Exploiting the optical/magnetic bifunctional upconversion nanoparticles (UCNPs) with small size has become a trend in the high-resolution biological imaging. Here, we report the simultaneous size manipulation and color tuning in Er 3+ -sensitized perovskite KZnF 3 UCNPs via Mn 2+ doping. It was found that the introduction of Mn 2+ into the KZnF 3 host matrix facilitates the reduction of the nanoparticle size (from 1 μm to 50 nm). Under the excitation of both 980 and 808 nm continuous wave (CW) laser, these KZnF 3 :Er 3+ /Mn 2+ (1/x mol%) UCNPs can efficiently generate tunable upconversion luminescence (UCL) and achieve pure red UCL as the Mn 2+ concentration reaches 30 mol%. It is suggested that the energy transfer (ET) processes between Er 3+ and Mn 2+ ions contribute to the single-band red UC emission, which was well supported by investigating the dependence of UCL intensity on the pump power and the decay lifetimes of 4 S 3/2 and 4 F 9/2 states of Er 3+ ions. In addition, the KZnF 3 :Er 3+ /Mn 2+ UCNPs have been used as the T 1 -weighted magnetic resonance imaging (MRI) agents, which exhibits a high optical contrast with the background. These features make the KZnF 3 :Er 3+ /Mn 2+ UCNPs promising for excellent dual-modal agents in UCL imaging and MRI.