Core–shell-like Y2O3:[(Tb3+–Yb3+), Li+]/CdZnS heterostructure synthesized by super-close-space sublimation for broadband down-conversion

Abstract

Combination with semiconductors is a promising approach to the realization of broadband excitation of light conversion materials based on rare earth compounds, to boost the energy efficiency of silicon solar cells. Cd_1−xZn_xS is a wide bandgap semiconductor with large exciton binding energy. By changing its composition, the bandgap of Cd_1−xZn_xS can be tuned to match the absorption of trivalent lanthanide (Ln) ions, which makes it a competent energy donor for the Ln³⁺–Yb³⁺ couple. In this work, we designed a clean route to a broadband down-converter based on a core–shell-like Y₂O₃:[(Tb³⁺–Yb³⁺), Li⁺]/Cd_0.81Zn_0.19S (CdZnS) heterostructure. By hot-pressing and subsequent annealing of a Y₂O₃:[(Tb³⁺–Yb³⁺), Li⁺]/CdZnS mixture, highly pure CdZnS was sublimated and deposited on the Y₂O₃:[(Tb³⁺–Yb³⁺), Li⁺] grains while maintaining the original composition of the precursor. The CdZnS shell acted as a light absorber and energy donor for the Tb³⁺–Yb³⁺ quantum cutting couple. Because the use of solvents was avoided during the formation of the heterostructures, few impurities were incorporated into the samples, and the non-radiative transition was therefore markedly suppressed. The Y₂O₃:[(Tb³⁺–Yb³⁺), Li⁺]/CdZnS heterostructures possess strong near-infrared (NIR) luminescence from Yb³⁺. Broadband down-conversion to the Yb³⁺ NIR emission was obtained in a wide range of 250–650 nm.