Electric Field-Tuned Polymer Amplified Spontaneous Emission

Abstract

After an external laser pulse/beam is used to pump a conjugated polymer, such as poly(phenylene vinylene) (PPV), the continuous optical pumping reverses the electron populations in a polymer light-emitting diode, leading to amplified spontaneous emission (ASE). This is accompanied by localized lattice distortion along the polymer chain due to the excitation of a singlet exciton. With the application of an electric field along the polymer, the inversion of electron population is weakened. Once the strength of the applied electric field exceeds a certain threshold, it leads to the aberrance of the localization contributed by the excitation of exciton, which not only forbids the electron transition, but quenches the ASE.Since the pioneering discovery of polymer/organic light emitting diodes (PLEDs/OLEDs) in the 1980s, 1-3 much progress has been made to improve the efficiency of PLEDs. Under external photoexcitation or charge injection, the electron in the highest-occupied molecular orbital (HOMO) binds with the hole in the lowest-unoccupied molecular orbital (LUMO) to form an exciton. The radiative decay of singlet excitons leads to the light emission of PLEDs/OLEDs. 4 With continuous external photoexcitation or pumping, the excitons are stimulated to result in electron population inversion and, subsequently, amplified spontaneous emission (ASE), even laser emission. 5 Based on this simple physical picture, Soffer et al. fabricated a laser based on dye-doped polymers in the 1960s. 6 Following that, Avanesjan et al. demonstrated the lasing effect on the basis of a single crystal of fluorine-doped anthracene. 7, 8 Up to 1992, the first polymeric semiconductor laser was developed in a solution consisting of a conjugated polymer. 9 Four years later, plastic polymers were extended to solid conjugated polymers. 10-13 Since then, conjugated polymer lasers with a variety of resonators, such as distributed feedback and photonic bandgap structures, have been extensively made by utilizing various coating and imprinting techniques. 14,15 When an electric field is applied to a PLED and exceeds a critical value, it dissociates the exciton to new carriers (charged polarons) and also quenches the luminescence. [16][17][18] Compared with the electric field-induced quenching of luminescence in a PLED, the question arose as to how the lasing effect is influenced by the external field, such as the bias voltage on the polymer laser. In order to answer this question, Zhang et al. utilized the strong electric field, and observed that, when the applied electric field approaches and exceed a threshold, ASE in poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene (MEH-PPV) thin film is weakened accordingly, and even quenched, similar to the electric field-induced quenching of luminescence of PLEDs. 19 Just by analogy between polymer ASE and polymer light-emitting diodes, this phenomenon is attributed to the previously-mentioned dissociation of excitons in a PLEDs thin film. 19 We recognize that the electronic structure of the exciton is j...

A novel synthesis of 4-toluene 9H-carbazole-9-carbodithioate, electropolymerization and impedance study

“…They have been suggested for a number of applications, such as electroluminescent devices [9], sensors [10,11], redox catalysts [12], and electrochromic displays [13]. The functional groups, such as amino, imino and sulfonic groups have been performed for achieving new polymers which meet the criteria of commercial applications [14][15][16].…”