Rewritable Triple-Mode Light-Emitting Display

Abstract

Despite great progress in developing mode-selective light emission technologies based on self-emitting materials, few rewritable displays with mode-selective multiple light emissions have been demonstrated. Herein, we present a rewritable triple-mode light-emitting display enabled by stimuli-interactive fluorescence (FL), room-temperature phosphorescence (RTP), and electroluminescence (EL). The display comprises coplanar electrodes separated by a gap, a polymer composite with FL inorganic phosphors (EL/FL layer), and a polymer composite with solvent-responsive RTP additives (RTP layer). Upon 254 nm UV exposure, a dual-mode emission of RTP and FL occurs from the RTP and EL/FL layers, respectively. When a polar liquid, besides water, is applied on the display and an AC field is applied between the coplanar electrodes, EL from the EL/FL layer is triggered, and the display operates in a triple mode. Interestingly, when water is applied to the display, the RTP mode is deactivated, rendering the display to operate in a dual mode of FL and EL. By manipulating the evaporation of the applied polar liquids and water, the mode-selective light emission of FL, RTP, and EL is rewritable in the triple-mode display. Additionally, a high-security full-color information encryption display is demonstrated, wherein the information of digital numbers, letters, and Morse code encoded in one optical mode is only deciphered when properly matched with that encoded in the other two modes. Thus, this article outlines a strategy to fulfill the substantial demand for high-security personalized information based on room-temperature multi-light-emitting displays.

Keywords: Alternating-current electroluminescence; Information encryption; Multimode luminescence; Room-temperature phosphorescence; Stimuli-responsive materials.

Fig. 1

Device architecture and working principles of RE-TriLED. a Exploded view layout of RE-TriLED. b Photograph of a RE-TriLED together with a polar liquid-soaked brush. c Cross-sectional SEM image of a RE-TriLED. d Mode-selective operation of the RE-TriLED and its possible emission modes: fluorescence (FL), room-temperature phosphorescence (RTP), and electroluminescence (EL). e Photographs of the emission modes of the RE-TriLED upon exposure to UV (254 nm) and AC field at its initial state (e4–e6), with H₂O (e1–e3), and with polar liquid (e7–e9). f Numerical simulations of electric field distribution of RE-TriLED with (right) and without (left) a polar electrode bridge (H₂O). g Normalized spectra of RTP, FL, and EL emissions. h Radial plot comparing the different characteristics of the light-emitting optical encryption platforms (see Table S2)

Fig. 2

Characterization of individual emission modes. a Photographs of FL and RTP films under UV irradiation (254 or 365 nm) and after removal of UV lamp. b-d Time-resolved photoluminescence (TRPL) decay profiles of FL (b), RTP (c), and FLʹ (d) emissions. e FL and RTP intensity upon exposure to various liquids. f RTP spectra of an RTP film heated at different temperatures after exposure to H₂O. g-i Luminance–voltage curves (g), normalized spectra (h), and CIE coordinates (i) of the EL emission as a function of AC frequency (polar-bridged by H₂O) together with the ones from FL, RTP, and FLʹ emissions. The solid lines in g are a fit to an exponential function. The insets in h are photographs of EL emission under AC frequencies from 0.1 to 30 kHz

Fig. 3

Mode-selective RE-TriLED with reversible RTP. a Schematic illustration of fabricating a RE-TriLED with a patterned RTP layer, and encryption process using H₂O and heat exposure. b, c Photographs of a RE-TriLED under UV irradiation and after removal of UV lamp without (b) and with (c) AC field. The RE-TriLED is also exposed to either H₂O or heat for reversible RTP emission. d Photographs of a RE-TriLED showing an encrypted number from zero to nine by treating H₂O on selective areas of the patterned RTP layer. e, f Overlay of normalized spectra (e) and CIE coordinates (f) of RTP, FL, and EL emissions for five heat-H₂O cycles. g RTP and EL emission wavelengths of a RE-TriLED upon repetitive H₂O and heat exposure (inset shows photographs of the RE-TriLED during the repeatability test)

Fig. 4

RE-TriLED with full visible RTP. a, b Normalized emission spectra (a) and CIE coordinates (b) of RTP, fluorescein-doped RTP (RTP-G), and rhodamine B-doped RTP (RTP-R) films together with the ones from EL and FL emissions. c TRPL decay profiles of RTP-G and RTP-R films. d Photographs of RTP-G and RTP-R films under UV irradiation and after removal of UV lamp. e, f Schematic illustration of a full-color RE-TriLED showing encrypted numbers by reversible RTP emission (e) and photographs of the full-color RE-TriLED exposed to UV and/or AC field (f). g Photographs of a full-color RE-TriLED showing different numbers encrypted upon repetitive heat-H₂O exposure

Fig. 5

Rewritable RE-TriLED with EL and RTP interplay. a Multilevel encryption of RE-TriLED with a patterned RTP layer using H₂O/ethylene glycol (EG) and EtOH/EG mixture. b Normalized EL area change upon exposure to H₂O, EtOH, or their mixtures with EG. c Schematic illustration of writing letters on a nonpatterned RE-TriLED. d Photographs of the RE-TriLED illustrated in c, exposed to UV and/or AC field. e Normalized RTP intensity upon repetitive exposure to H₂O/EG or EtOH/EG mixture

Fig. 6

Rewritable multilevel encryption of RE-TriLED array. a Left: exploded view layout of pixelated RE-TriLED array. Right: possible combinations of layers and their response to UV and AC field. b Schematic illustration of fabricating RE-TriLED arrays programmed with Morse code (b1) and its rewritability by removal of RTP and protective layer (b2). Real information is shown only when the RE-TriLED is exposed to all three stimuli. c Cases for the rewritable RE-TriLED array. c1 Photographs and schematic illustrations of the RE-TriLED array illustrated in b1, where the display is exposed to UV, UV and AC, UV and H₂O, and all together. c2 Photographs and schematic illustrations of the RE-TriLED array after its second programming, where the display is exposed to UV, UV and AC, UV and H₂O, and all together