Near-infrared to visible photon upconversion in Mn and Yb containing materials

Near-infrared (NIR) laser excitation into the Yb^{3+ 2}F_7/2→²F_5/2 absorption transition around 10,200 cm^?1 at 12 K leads to red and green upconversion emission in MnCl₂:Yb³⁺ and Zn₂SiO₄:Yb³⁺; Mn²⁺, respectively. The photon upconversion (UC) emission is centered around 15,240 cm^?1 for MnCl₂:Yb³⁺ and around 19,050 cm^?1 for Zn₂SiO₄:Yb³⁺; Mn²⁺ and is ascribed to the Mn^{2+ 4}T₁→⁶A₁ transition in both compounds. The shift of the Mn²⁺ emission energy is due to the different coordination and ligand strength. Pulsed measurements indicate a sequence of ground-state absorption (GSA) and excited-state absorption (ESA) steps for the upconversion process. We conclude that the UC process in both compounds occurs by an exchange mechanism involving Yb³⁺ and Mn²⁺ ions. Zn₂SiO₄:Yb³⁺; Mn²⁺ is the first example of a Yb³⁺–Mn²⁺ upconversion system to show visible (VIS) by eye Mn²⁺ UC emission at room temperature.