Controllable synthesis and multifunctional application of NaLaS2:Ln3+ nanoparticles in the second near-infrared region

Near-infrared two-zone (NIR-Ⅱ,1000–1700 nm) luminescent nanocrystals (NCs) doped with lanthanum ions (Ln 3+ ) exhibit considerable potential in multiple technological fields. ALnS 2 (A = Na, K, Rb; Ln = La–Lu, Y) is expected to be an efficient matrix material due to its low cell symmetry, strong covalence, and low phonon energy. Here, we synthesized NaLaS 2 :Ln 3+ NCs doped with Nd 3+ , Yb 3+ , and Er 3+ by the high-temperature co-precipitation method, and their NIR luminescence characteristics were studied in detail. The addition of N, N-diphenyl thiourea can effectively alter the size of NaLaS 2 :Ln 3+ NCs. Under different excitation (ex = 808 and 980 nm), strong NIR-Ⅱ luminescence and temperature sensitivity were achieved in Nd 3+ single-doped, Yb 3+ /Er 3+ co-doped, and Nd 3+ /Yb 3+ /Er 3+ co-doped NaLaS 2 NCs, respectively. We found that the maximum relative temperature sensitivity of NaLaS 2 :Nd 3+ in the NIR-Ⅱ region is 0.72 % K −1 @140 K. The luminescence of NaLaS 2 :Yb 3+ /Er 3+ NCs in the NIR-Ⅱ region is not sensitive to temperature changes, but after adding Nd 3+ as a sensitizer, its NIR-Ⅱ region luminescence has a good temperature sensitivity (0.11 % K −1 @240 K). In addition, we coated the nano NIR material onto the surface of different materials, which can present a clear fingerprint under the near-infrared camera; using the orthogonal emission of Ln 3+ , nano-near-infrared materials show different information under different excitations, which shows its role in detection and information anti-counterfeiting.