Intense blue-emitting Yb/Tm-CaSiO3 wollastonite upconversion phosphors

Abstract

Wollastonite is a naturally occurring mineral with a chemical formula of CaSiO3. Owing to outstanding mechanical, chemical, and thermal stabilities, wollastonites have become one of the most versatile industry minerals for applications in construction materials, cement, plastics, paints and coatings, friction, automobile brakes, ceramic and metallurgical applications to name a few. Despite technological importance, research on functional properties such as photon upconversion in wollastonites is still lacking. In this report, an initiative has been taken to demonstrate ultra-violet, blue, and near-infrared photon upconversion in CaSiO3 wollastonite via Yb and Tm doping. The wollastonite ceramics are synthesized via microwave hydrothermal technique followed up by heat-treatment in air. β-wollastonite (2M) phase in the synthesized samples has been confirmed by X-ray diffraction and a successful doping of Yb3+ and Tm3+ ions in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The most intense phonon band has been observed at 872 cm−1. Upon 980 nm excitation, ultraviolet, intense blue, and near-infrared upconversion emissions as well as downshifting infrared emissions are observed from Tm3+ ions as a result of sensitization by Yb3+. The temporal evolution of the emitting states is studied to understand the emission mechanism. An absolute upconversion quantum yield of the 20Yb/0.5Tm–CaSiO3 sample in the 400–850 nm range is 0.79%.