X-ray radioluminescent (XRL) crystalline colloidal arrays (CCAs) with highly tunable emission colors are synthesized using an emulsion polymerization procedure. An anthracene methyl methacrylate derivative (AMMA) is copolymerized within a poly(styrene-co-propargyl acrylate) basis to generate an XRL CCA, emitter 1 (E1). Due to the electrostatic repulsive forces between the colloidal nanoparticles, E1 spontaneously self-assembles into an FCC structure. E1 possesses a stop-band (i.e., rejection wavelength) corresponding to specific wavelengths of light where propagation through the crystal is forbidden. The rejection wavelength is located in the visible regime and can be shifted across the visible spectrum by a change in the interplanar spacing of the colloid, which is achieved by the addition or removal of deionized water. Typical anthracene emission, is detected when there is no rejection wavelength interference. However, a decrease in spontaneous emission at the rejection wavelength is observed when the rejection wavelength is shifted within E1’s XRL. XRL decrease corresponding to the rejection wavelength can be shifted across the entire emission of E1. In this way, the CCA’s emission can be manipulated by photonic means. Furthermore, the CCA’s color characteristics can be adjusted across the visible spectrum by x-ray induced sequential Förster Resonance Energy Transfer (FRET). Energy transfer is achieved by copolymerizing one or two additional organic fluorophores that form FRET pairs with AMMA and each other. A naphthalimide methyl methacrylate derivative (NMMA) that absorbs in the blue region where AMMA emits is incorporated within E1 to generate a green-emitting XRL CCA, emitter 2 (E2). Additionally, a rhodamine B methyl methacrylate derivative (RMMA) that absorbs in the green region where NMMA emits is incorporated within E2 to generate a red-emitting XRL CCA, emitter 3 (E3). In this way, x-ray induced FRET or x-ray induced sequential FRET is achieved, respectively. The rejection wavelength of E2 and E3 can be coupled with their XRL to fine-tune the color characteristics of the liquid systems. Moreover, nanophotonic manipulation of the x-ray induced FRET between emitters was observed in E3, where the FRET efficiency between two emitters could be increased or decreased by suppressing the donor or acceptor’s emission via the rejection wavelength, respectively.

Manipulating color characteristics via x-ray induced sequential Förster resonance energy transfer and a photonic bandgap in a radioluminescent crystalline colloidal array

ACS Spring 2022

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