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In this study, fluorescent nitrogen-doped carbon dots (NCDs) were tuned via varying the sources with different number of carboxyl groups. Owing to the interaction between amino and carboxyl, more amino groups conjugate the surface of the NCDs by the source with more carboxyl groups. Fluorescent NCDs were tuned via varying the sources with different content of carboxyl groups. Correspondingly, the nitrogen content, fluorescence quantum yields and lifetime of NCDs increases with the content of carboxyl groups from the source. Furthermore, cytotoxicity assay and cell imaging test indicate that the resultant NCDs possess low cytotoxicity and excellent biocompatibility.

NaGdF4: A (A = Eu, Tb)@NaGdF4: Yb, Tm@NaGdF4: Yb, Nd core–shell–shell is designed to achieve 808 nm excited upconversion emission tuning. On the basis of the above core–shell–shell nanostructure, intense upconversion emission has been realized for activators without long-lived intermediate states (Eu3+, Tb3+) through Gd3+-mediated energy migration under 808 nm irradiation, enriching the emission colors. The spatial separation, where sensitizer (Nd3+), accumulator (Tm3+), and activator (Eu3+, Tb3+) are doped into separated layers, effectively suppresses nonradiative decays so that the doping concentration of Nd3+ can reach to 40%, vastly enhancing the luminescence intensity. Notably, when Gd3+ ions are replaced by Nd3+ or inert Y3+ in NaGdF4: Yb, Nd outer shell, without Gd3+-mediated energy migration, the deleterious energy transfer from Tm3+ in the interlayer to surface quenchers is suppressed, and thus, more active energy is trapped by activators, which induces the further change of upconversion emission color. Furthermore, the multicolor upconversion tuning can also be realized via Tb3+-mediated energy migration. 808 nm excited multicolor upconversion tuning, overcoming low tissue penetration and overheating effect under 980 nm excitation, improves the feasibility of upconversion nanoparticles in multicolor imaging and multiplexed detection areas.

The detection of ultraviolet (UV) radiation with effective performance and robust stability is essential to practical applications. Metal halide singlecrystal perovskites (ABX 3 ) are promising next-generation materials for UV detection. The device performance of all-inorganic CsPbCl 3 photodetectors (PDs) is still limited by inner imperfection of crystals grown in solution. Here wafer-scale single-crystal CsPbCl 3 thin films are successfully grown by vapor-phase epitaxy method, and the as-constructed PDs under UV light illumination exhibit an ultralow dark current of 7.18 pA, ultrahigh ON/OFF ratio of ≈5.22 × 10 5 , competitive responsivity of 32.8 A W −1 , external quantum efficiency of 10867% and specific detectivity of 4.22 × 10 12 Jones. More importantly, they feature superb long-term stability toward moisture and oxygen within twenty-one months, good temperature tolerances at low and high temperatures. The ability of the photodetector arrays for excellent UV light imaging is further demonstrated.