RETRACTED: Sensitization of Lanthanides with Metal Chalcogenides Nanocrystals: Night Vision Imaging and Security Encryption

Abstract The sensitization of lanthanide ions by semiconductor nanocrystals offers promising potential for developing luminophores with high quantum yields, promising for light harvesting and imaging applications. This study introduces lanthanide‐doped CdS nanocrystals fabricated through a phosphine‐free method. Lanthanide ions such as Yb 3+ , Tm 3+ , Ho 3+ , and Er 3+ are successfully doped into the CdS matrix, resulting in tunable NIR emissions ranging from 950 to 1600 nm. These nanocrystals exhibit visible–NIR emission with a total photoluminescence quantum yield of ≈41 ± 3%. Steady‐state and time‐resolved spectroscopic studies confirm the broadband sensitization of lanthanide ions by the CdS host. Binary ions‐doped CdS nanocrystals (CdS:Yb 3+ , Er 3+ /Ho 3+ /Tm 3+ ) demonstrate both upconversion and downshifting processes within a single system. Furthermore, the NIR emission is enhanced under CdS excitation compared to direct lanthanide sensitization. Time‐resolved photoluminescence and transient absorption studies reveal the efficient energy transfer processes from CdS to the lanthanide dopants. Additionally, the NIR emission in CdS:Ln 3+ embedded polymethyl methacrylate nanocomposites remains highly stable even months after fabrication, making them suitable for night vision imaging and security encryption. This study, therefore, advances the development of smart visible‐to‐NIR light sources for optoelectronic applications, including enhanced anti‐counterfeiting measures and night vision imaging.