Spectrally Narrowed Edge Emission from Organic Light-Emitting Diodes: Evidence for Amplified Spontaneous Emission and Mirrorless Lasing

TL;DR

This paper presents evidence of amplified spontaneous emission and mirrorless lasing in electrically driven small molecular organic LEDs, showing spectral narrowing and optical gain at room temperature, advancing the development of organic diode lasers.

Contribution

It provides the first evidence of ASE and mirrorless lasing in DC-driven small molecular organic LEDs, highlighting spectral narrowing and optical gain without a clear lasing threshold.

Findings

Spectral line narrowing to 5-10 nm FWHM in SMOLEDs.

Detection of optical gain in edge-emission at room temperature.

No definitive threshold behavior observed for lasing.

Abstract

p-Conjugated materials, including small molecules and polymers, are attracting substantial attention as novel gain media in semiconductor lasers; they offer many potential advantages not achievable with conventional inorganic semiconductors: simple processing, low cost, easy tuneability of the spectrum, and large-area integration on flexible substrates. Optically pumped lasing action in various small molecular and polymeric p-conjugated materials has been demonstrated using several resonator configurations. However, electrically pumped organic semiconductor lasers, i.e., organic injection or diode lasers, remain elusive, presumably due to various loss mechanisms, e.g., charge (polaron)-induced absorption and metal electrode absorption. Here we report on evidence for amplified spontaneous emission (ASE), also known as mirrorless lasing (i.e., wherein some of the spontaneously emitted photons are amplified by stimulated emission during their propagation) in DC-driven small molecular organic light-emitting diodes (SMOLEDs). The evidence includes a dramatic spectral line narrowing, with a full width at half maximum (FWHM) of only 5 - 10 nm, and optical gain, of the edge-emission from SMOLEDs at room temperature. However, there is no clear indication of threshold behavior associated with this spectral narrowing. Nevertheless, this discovery should pave the way towards the realization of an organic diode laser.