Down‐/Upconversion Luminescence Properties and Anti‐Counterfeiting Applications of Lu ₂ O ₃ :Tm,Yb and Lu ₂ O ₂ S:Tm,Yb Phosphor Powders

In this work, a Lu 2 O 3 precursor was synthesized via the chemical coprecipitation method. This precursor was subsequently sulfurized in a hydrogen atmosphere at 950°C, yielding a two‐dimensional layered Lu 2 O 2 S:Tm, Yb powder with a thickness of several micrometers. The optimal doping concentrations for the Yb 3+ sensitizer were determined to be 5% and 10% for the oxide and oxysulfide, respectively. Under excitation with a 980‐nm laser pump, the oxide powder displayed strong blue emission in the visible region (450–510 nm, attributed to the 1 G 4 → 3 H 6 transition of Tm 3+ ) and weak red emission (650–670 nm, from the 3 F 2 → 3 H 6 transition of Tm 3+ ). Notably, the oxysulfide powder not only exhibited strong blue and red emission but also intense green emission (530–560 nm, corresponding to the 1 D 2 → 3 H 5 transition of Tm 3+ ). The upconversion process was primarily a two‐photon absorption mechanism. The fluorescence lifetimes for the blue emission of the oxide powder and the near‐infrared emission of the oxysulfide powder were ≈0.42 and 2.17 ms, respectively. This work systematically investigated the down‐/upconversion properties of the two types of powders. The synthesized oxysulfide powder, characterized by high luminescence intensity, demonstrates potential as a dual‐mode anti‐counterfeiting material.