Advantages of naphthalene as a building block for organic solid state laser dyes: Smaller energy gaps and enhanced stability

Organic laser dyes exhibiting very low amplified spontaneous emission (ASE) thresholds in green and yellow regions were developed based on a stilbene structure which is often used for the blue laser molecules. Although the thresholds are generally increased with decreasing energy levels of molecules, the introduction of a naphthalene unit can shift the emission colors without sacrificing optical properties. In particular, the suppression of concentration quenching by naphthalene moieties resulted in high radiative decay rate constants and low ASE thresholds in the neat films. In addition, the photo- and thermal-stabilities of the naphthalene derivatives were improved compared to those of the corresponding phenylene derivatives. This study demonstrates a simple and effective molecular design for developing green and yellow laser dyes by a small modification from the standard blue emitters.