INFRARED–VISIBLE LIGHT CONVERSION USING DCM DYE MICROGRAINS EMBEDDED IN A RESIN SHEET AND APPLICATION TO AN IR SENSOR CARD

摘要

We report high-efficiency visible light emission(λ=600–690 nm) from aggregated 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye micrograins excited by infraredlight (λ_(ex) = 805 nm). The light-emitting regions werelocalized at the surfaces and edges of the micrograins,where the optical near-field was more intense. This hasbeen theoretically explained by exciton?phononpolaritons, i.e., the dressed photon model, in which anelectron is excited due to a multistep transition via anintermediate phonon state coupled with a localizedexciton polariton (a dressed photon). The lifetime(about 1 ps) of the intermediate state has beenmeasured by the pump–probe method. We prepared aresin sheet containing the DCM and identified theorigin of the intermediate state as an O-H stretchingvibration mode, by time-resolved Raman spectroscopyusing a 10 fs pulsed laser as an excitation light source.As the molecules aggregated, the emission efficiencywith visible light excitation (λ＜550 nm) decreased, i.e.,concentration quenching, whereas the emissionefficiency with infrared excitation increased. This isbecause a broad O-H phonon band with strongoscillator strength is created by hydrogen bonds amongthe molecules, acting as an efficient intermediatephonon state for the multistep transition. An IR sensorcard was also demonstrated.