Multicolor tunable luminescence and laser-sensitization induced upconversion enhancement in Ln-doped Gd2O3 crystals for anti-counterfeiting

Abstract

Upconversion materials endow great potential in converting infrared irradiation to visible luminescence for security anti-counterfeiting applications. However, the development and application of upconversion materials are constrained greatly by their underlying shortcomings such as single emission colors, and low emission brightness. Here, a new approach to rationally engineering upconversion matrices with desirable performance and particle morphology is presented in Gd₂O₃:Er³⁺,Yb³⁺ nanocrystals, which leads to significant enhancement of luminescence signals (up to 409 folds) and flexibly tunable UC colors. The laser-sensitization upconversion emission is systemically studied under the excitation of a 980 nm single NIR light source. We identify that the laser induced-synergic effect, crystal morphology evolution and unlocking dark sensitizers are the key factors underpinning this enhancement. Importantly, owing to this special laser power dependent optical property, these materials represent a convenient route for high security anti-counterfeiting applications. These results not only provide an upfront simple experimental design for constructing upconversion materials with strong luminescence and color tunability, but also deepen the understanding of the interaction mechanism between lasers and upconversion emission, which may be very important for practical applications in anti-counterfeiting.