Optical Properties Investigation of Upconverting KGd(PO)(WO):20%Yb,Tm Phosphors.

Nowadays, scientists are interested in inorganic luminescence materials that can be excited with UV or NIR radiation and emit in the visible range. Such inorganic materials can be successfully used as luminescent or anti-counterfeiting pigments. In this work, we report the synthesis and optical properties investigation of solely Tm doped and Yb/Tm co-doped KGd(PO)(WO) phosphors. The single-phase samples were prepared using a solid-state reaction method. The Tm concentration was changed from 0.5% to 5%. Downshifting and upconversion emission studies were performed under 360 nm and 980 nm excitation, respectively. Yb ions were used as sensitizers in the KGd(PO)(WO) phosphors to transfer the captured energy to Tm ions. It turned out that under UV excitation, phosphors emitted in the blue spectral area regardless of the presence or absence of Yb. However, a very strong deep-red (~800 nm) emission was observed when Yb and Tm-containing samples were excited with a 980 nm wavelength laser. It is interesting that the highest upconversion emission in the UV/Visible range was achieved for 20% Yb, 0.5% Tm doped sample, whereas the sample co-doped with 20% Yb, 2% Tm showed the most intensive UC emission band in the NIR range. The materials were characterized using powder X-ray diffraction and scanning electron microscopy. Optical properties were studied using steady-state and kinetic downshifting and upconversion photoluminescence spectroscopy.