Highly dispersed spherical phosphors obtained by encapsulating silica hollow spheres with SnO2: Eu3+ layers for enhancing red light emission

Abstract

Orange light (593 nm, 5D0→7F1) and red light (613 nm, 5D0→7F2) are the two most important emission lines belonging to Eu3+ ions in high and low symmetries, respectively, making them important indicators for judging the nanoenvironment around Eu3+ ions. Therefore, obtaining significant red light emission in Eu3+ doped SnO2 nanocrystals requires anchoring Eu3+ ions onto lattice sites with low symmetries, which can be achieved through maximizing surface doping. To achieve this goal, we coated very thin Eu3+ doped SnO2 nanocrystal (10–20 nm) coatings on extremely dispersed SiO2 hollow spheres (500 nm in diameter) to investigate doping dependent luminescent properties. A significant increase in red emission was observed in such a system, accompanied by a significant attenuation of orange light, and the intensity of red emission increases with increasing Eu3+ concentration. When the concentration of Eu3+ exceeds 3 at%, the intensity of red light emission sharply decreases due to the quenching effect. For the optimal doped hollow sphere sample (3 at%), the asymmetry ratio (red/orange light integration intensity ratio) under indirect excitation is 5.58, which further rises to 11.3 under direct excitation, while the asymmetry ratio of SnO2 nanopowder with the same doping concentration is less than 0.2 under both excitation modes, indicating that the current structural design plays a significant role in the modulation of Eu3+ ion luminescence. Our research not only demonstrates an effective method to enhance the red light emission of Eu3+ doped SnO2 nanocrystals, but also provides a method for manipulating the polychromatic luminescence of such systems.