Synthesis of hollow La2O3:Yb3+/Er3+/Tm3+ microspheres with tunable up-conversion luminescence properties

Abstract

Hollow La2O3:Ln3+ (Ln3+ = Yb3+, Er3+, Tm3+) microspheres were successfully synthesized via a facile sacrificial template method by employing PS spheres as hard template followed by a subsequent heating process. The structure, morphology, and formation process are well investigated by various techniques. A systematic study on the up-conversion (UC) PL properties of La2O3:Yb3+/Er3+/Tm3+ products have been performed in detail. Under 980 nm laser diode excitation, La2O3:Yb3+/Tm3+, La2O3:Er3+ and La2O3:Yb3+/Er3+ products are mainly dominated by blue, green, and red light emissions, respectively. By increasing Er3+ concentration, the La2O3:Er3+ gives yellow emission. Furthermore, the UC white light was successfully obtained in the La2O3:Yb3+/Er3+/Tm3+ system by adjusting the relative doping concentration of Yb3+, Er3+ and Tm3+. The obtained UC white light can be tuned at a wide range, and the optimal white-emitting CIE (Commission internationale de l'eclairage [International Commission on Illumination]) chromaticity coordinate is (x = 0.3250, y = 0.3180), which is very close to the standard equal energy white light (x = 0.33, y = 0.33). The strategies for color tuning of up-conversion emission proposed in the current system may be helpful for other ones to achieve efficient multicolor (including white light) luminescence under 980 nm laser excitation. Because of abundant luminescent colors from RGB to white in La2O3:Yb3+/Er3+/Tm3+ samples under 980 nm laser diode (LD) excitation, they can potentially be used as fluorophores in the field of color displays, back light, UC lasers, and photonics.