Effect of Ti compositions for efficiency enhancement of CaTiO3:Er3+,Ni2+ broadband-sensitive upconverters

Abstract

Improving the efficiency of upconversion (UC) materials is a hot topic in recent days due to the important applications of UC materials in photovoltaics, photonics devices, photocatalysts, sensors, biological imaging, and therapeutics. Recently, we have reported a broadband-sensitive UC emission in Ni²⁺, Er³⁺-codoped perovskites. However, the applications of these perovskites are limited due to their low conversion efficiency. Herein, we realized highly improved UC efficiency in the CaTiO₃:Er³⁺,Ni²⁺ upconverter as compared to those of the previously reported CaZrO₃ and La(Ga,Sc)O₃ upconverters. Ti composition plays important roles in stabilizing divalent nickel (Ni²⁺) in an octahedral coordination, which is the key point for sensitization to Er³⁺ emitters. Furthermore, oxygen vacancies and consequently tetrahedral Ni²⁺ ions, which kill the luminescence, are suppressed, and as a result, the UC emission intensity is dramatically increased. The 0.1 mole Ti-deficient sample with the (Ca_0.8Er_0.10Li_0.10)(Ti_0.894Ni_0.002Nb_0.004)O_2.8 composition exhibited the most intense broadband-sensitive UC emission, which was 264-fold stronger than that of the stoichiometric sample and more than 12 folds as compared to that of the previously reported CaZrO₃:Er,Ni and La(Ga,Sc)O₃ upconverters. The highest UC quantum yield of ∼2.53% was realized in the optimized CaTiO₃:Er³⁺,Ni²⁺ upconverter under 1490 nm laser excitation of ∼1000 W m⁻².