Room temperature phosphorescent (RTP) carbon dots have attracted considerable interest due to their fundamental importance and potential applications in optoelectronic devices, sensing, bioimaging and document security. The preparation method of RTP carbon dots is based on the formation of the CN (or CO) groups and hydrogen bond. Herein, we have added acrylamide in the reaction system to form hydrogen bonds and stabilize the triplet excitons. Thus, the nontoxic RTP carbon dots (NCDs) were designed and prepared via a one-step hydrothermal method. The nitrogen element (N) in the NCDs can effectively increase their fluorescence intensity, while the produced CN bonds promote the formation of triplet excitons. More importantly, the acrylic amide and the as-generated polyacrylamide (PAM) on the surface of NCDs could easily connect with the as-prepared pyridinic N via the reaction between citric acid and urea, and formed the hydrogen bond that could stablilize the triplet excitons. Hence, NCDs exhibit stable phosphorescence properties. We further show the promising application of the as-prepared aqueous NCDs as a new smart concealed and potential security ink.

CsPbBr₃@Ag hybrid nanocrystals are synthesized, where photoluminescence was significantly enhanced by localized surface plasmons of Ag nanoparticles.

The ability to tune the emission color of upconversion nanoparticles (UCNPs) will greatly enhance the scope of their applications, ranging from infrared solar cells to volumetric multiplexed bioimaging. Conventional methods to tune upconversion are to vary the type and/or the concentration of doped rare-earth ions in these nanoparticle formulations. Here, we introduce a different approach to vary the emission colors of the frequently used sensitizer/activator pairs of Yb³⁺/RE³⁺ (RE = Ho, Er, Tm) via utilization of a sensitizer/activator-isolated NaYF₄ core–shell structure. We show that the typical green, yellow, and blue luminescent colors from Yb³⁺/Ho³⁺-, Yb³⁺/Er³⁺-, and Yb³⁺/Tm³⁺-co-doped NaYF₄ UCNPs can be converted into the quasi-white, green, and pink blue, when corresponding core–shell structures of NaYF₄:Yb³⁺ @NaYF₄:Ho³⁺, NaYF₄:Yb³⁺ @NaYF₄:Er³⁺ and NaYF₄:Yb³⁺ @NaYF₄:Tm³⁺ are built. Time-resolved spectra indicate that decay lifetimes of the emission bands from the sensitizer/activator-isolated core–shell structure significantly vary from that of the sensitizer/activator-codoped NaYF₄ UCNPs, verifying the strain-induced modulation of emission channels in the core–shell structure. These sensitizer-activator-isolated core–shell UCNPs have implications for a range of biophotonic or photonic applications.