Stimulus Modulation of White Light Emission in Colloidal Polymer Nanoparticles by Fluorescence Resonance Energy Transfer for Temperature Sensing and Security Encryption

Dual temperature- and photoresponsive polymer nanoparticles with sensitivity toward temperature variation through fluorescence resonance energy transfer (FRET)-assisted white light emission (WLE) were synthesized using distillation–precipitation polymerization. A fluorescence chemosensor of temperature, white light-emitting anticounterfeiting inks, and different products for security encryption of confidential documents were prepared on the basis of the FRET mechanism due to an efficient spectral overlap between the emission of the coumarin donor and the absorption of the rhodamine B (RhB) acceptor. At the 150 μL RhB doping, a strong WLE was observed as a consequence of the FRET mechanism between the two complementary colors. Upon increasing the temperature in the range of 25–85 °C, the efficient FRET distance was affected due to squeezing of the thermoresponsive polymer moieties in response to heating; thus, FRET was turned off. These stimulus-responsive fluorescent nanoparticles were finally used as temperature sensors and in security encryption applications by incorporating on/off WLE based on the FRET mechanism and the preparation of white light-emitting paper, silk, and ink through the incorporation of FRET species into paper pulp, impregnation of silk in the colloidal fluorescent nanoparticles, and adding poly(ethylene glycol) and glycerol to the polymer colloids, respectively.