Mechanism of one- and two-photon absorption induced photoluminescence in PPV type, electroluminescent polymer

• Published in: Optics communications Vol. 203; no. 1; pp. 151 - 157
• Main Authors: Joon Lee, Geon, Kim, Kyungkon, Jin, Jung-Il
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-03-2002; Elsevier Science
• Subjects: Applied sciences; CzEH-PPV; Electrical, magnetic and optical properties; Electroluminescence; Exact sciences and technology; Exciton lifetime; Organic polymers; Photoluminescence excitation; Physicochemistry of polymers; Properties and characterization; Selection rule; Spectrally narrowed emission; Two-photon absorption; Spectrally narrowed emission; CzEH-PPV; Photoluminescence excitation; Two-photon absorption; Electroluminescence; Selection rule; Exciton lifetime; Exciton; Photoluminescence; Photoinduced effect; Phenylenevinylene derivative polymer; Experimental study; Mechanism; Luminescence decay; Conjugated polymer; Lifetime; Optical properties; Carbazole derivative polymer; Excitation spectrum; Two photon absorption
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/S0030-4018(02)01080-5

We report the luminescence properties in a poly(phenylenevinylene) derivative with the carbazole pendent and alkoxy group (CzEH-PPV). The two-photon excitation spectrum showed that the threshold energy
(2ℏω=2.64
eV)
of two-photon absorption (TPA) is larger than that (2.34 eV) expected by one-photon excitation spectra. This implies that the two- and one-photon absorptions satisfy different selection rules. Meanwhile, the two- and one-photon absorption (OPA) induced photoluminescences (PLs) were found to occur from the same exciton band that has a double minimum adiabatic potential. The lifetimes of the upper and lower exciton states are measured to be 280 and 370 ps, respectively. By comparing the PL spectrum of CzEH-PPV film to its electroluminescence spectrum of single-layer CzEH-PPV light-emitting device (ITO/CzEH-PPV/Al), the species generated by OPA or TPA are found to be the charged carriers. For OPA-PL, the excitations having the pulse-energy larger than
2.3
μ
J at 2.96 eV produce a spectrally narrowed emission band with its maximum located at 2.14 eV with the spectral width of 23 meV. This is ascribed to the amplified spontaneous emission enhanced by the optical wave guiding in the polymer film.