MoS₂ is an important two-dimensional transition metal dichalcogenide (TMD), whose physical and chemical properties are closely related to its layer number, size, defects, and crystal structure. Therefore, the controllable synthesis of phase-pure monolayer MoS₂ represents a key challenge. Herein, we report a simple and efficient wet-chemical synthesis strategy for 1T-MoS₂ and 2H-MoS₂, with the crystal phase controlled by the reaction temperature. At 220 °C, ultra-small (1–2 nm) monolayer 1T-MoS₂ colloids are obtained; at 250 °C, monolayer 2H-MoS₂ nanosheets are produced. Both materials exhibit good dispersibility in nonpolar solvents and can be readily spin-coated into thin films. Interestingly, the 1T-MoS₂ and 2H-MoS₂ exhibit different exciton dynamics in transient absorption (TA) spectra, but similar trap state-induced negative photoconductivity (NPC) under near-infrared (825 nm) illumination. These findings provide new perspectives for the design of MoS₂-based optoelectronic devices.

Despite recent progress, it remains challenging to fabricate stable deep blue-emitting perovskites. Here, we propose a molecular etching strategy to obtain ultra-small CsPbBr₃ perovskite quantum dots (QDs) with robust deep-blue emission. The diphenylalanine (FF) with high polarity is used to break ionic bonds of CsPbBr₃ to strip off atomic layers from the QDs. Simultaneously, perfluoroglutaric acid (PFGA) ligands are employed to passivate the QDs surface, effectively overcoming the surface defects induced by ligand detachment. By adjusting the volume ratio of QD:FF solutions, the emission wavelength can be continuously tuned from 506 to 458 nm, yielding deep-blue emission with high color purity. Comprehensive analyses using transient absorption, time-resolved photoluminescence (PL), and temperature-dependent PL measurements indicate that the emission blueshift is primarily attributed to the enhanced quantum confinement effects resulting from the reduced size. Furthermore, a dual-level optical encryption strategy is proposed by leveraging the intrinsically higher photostability of ultra-small CsPbBr₃ than that of mixed halide CsPb(Cl/Br)₃ QDs. This work provides a viable pathway for fabricating high-efficiency, ultra-stable deep-blue emitting perovskite QDs, showing significant potential for advanced applications in high-resolution displays and optoelectronic encryption.

Luminescent materials with multi-emission features are difficult to be replicated, which are highly desirable for advanced anti-counterfeiting. Here, we report the pioneering synthesis of Mn²⁺/Yb³⁺/Er³⁺ tri-doped Cs₂Ag_0.8Na_0.2InCl₆ double perovskites (MYE-DP), which exhibit photoluminescence (PL) covering from visible to near-infrared (NIR). The PL colors under excitations of 254 and 365 nm are notably different due to the changed relative emission intensities of self-trapped excitons (STEs) and Mn²⁺ d–d transition. Moreover, under the excitation of a NIR laser, the MYE-DP exhibits upconversion (UC) emissions of Mn²⁺ and Er³⁺. After ceasing the excitation, the long-lived trapped electrons can be thermally released to Mn²⁺ and Er³⁺ ions, resulting in both visible and NIR afterglow. Based on multi-modal emissions of the MYE-DP, we demonstrate a five-level anti-counterfeiting strategy, which significantly increases the anti-counterfeiting security. In addition, this work provides valuable insights into the energy transfer between STEs, Mn²⁺, Ln³⁺, and traps, laying a solid foundation for future development of new lead-free perovskites.

Carbon nitrides synthesized by thermal polycondensation of melamine at 700 ℃ exhibit photoluminescence (PL) ranging from 400 to 650 nm. This broad PL is attributed to band to band transitions and bandtail transitions of lone pair (LP) states of intra-tri-s-triazine and inter-tri-s-triazine nitrogens. The proposed PL mechanism is further confirmed by diffusion reflectance spectroscopy, as well as time-resolved and temperature-dependent PL. This intense fluorescence is stable at different pH and resistant to UV exposure, suggesting that this inexpensive broadband luminescent material could be significant for whitelight-emitting (WLE) applications. Thus, quasi-WLE films and membranes with designed patterns are fabricated by embedding the carbon nitrides into polymethyl methacrylate. Moreover, even broader PL (400 to 740 nm) is acquired in composite films composed of carbon nitrides, further suggesting that the carbon nitrides are robust candidates for WLE.