Controlling Er multiphoton upconversion by synergistically regulating energy transfer and cross-relaxation for optical anti-counterfeiting.

The synergistic effect of various ions with optical properties is an important method to regulate the Er ion upconversion luminescence process. However, the energy processes between them are complicated and difficult to separate, and it is challenging to clarify the results of each process when multiple ions are co-doped. Herein, a series of NaYF:Er were synthesized by the low-temperature combustion method, and the luminescence color of Er ions was modulated by doping Yb ions and Tm ions. The luminescence characteristics of the samples were studied by means of UC luminescence spectra and decay curves, and the luminescence mechanisms at different excitation wavelengths were discussed by the intensity-power test. Yb ions acted as energy transfer centers to regulate the color of Er ions, while Tm ions acted as cross-relaxation centers to influence the upconversion energy process of Er ions. Under the coordinated induction of Yb and Tm ions, the optimal red-light emission of Er ions was achieved under 980 nm and 1550 nm excitation. Multiple excitation modes regulated multiple upconversion energy processes, and this series of phosphors exhibited multicolor upconversion luminescence performance, which is expected to be applied in the field of advanced optical anti-counterfeiting. This work provides a new idea for the study of upconversion energy process separation, and it is helpful to promote the design and development of high color purity upconversion phosphor material systems.