Dual Amplified Spontaneous Emission and Lasing from Nanographene Films

Abstract

Chemically synthesized zigzag-edged nanographenes (NG) have recently demonstrated great success as the active laser units in solution-processed organic distributed feedback (DFB) lasers. Here, we report the first observation of dual amplified spontaneous emission (ASE) from a large-size NG derivative (with 12 benzenoid rings) dispersed in a polystyrene film. ASE is observed simultaneously at the 685 and 739 nm wavelengths, which correspond to different transitions of the photoluminescence spectrum. Ultrafast pump-probe spectroscopy has been used to ascertain the underlying photophysical processes taking place in the films. DFB lasers, based on these materials and top-layer nanostructured polymeric resonators (i.e., one or two-dimensional surface relief gratings), have been fabricated and characterized. Lasers emitting close to either one of the two possible ASE wavelengths, or simultaneously at both of them, have been prepared by proper selection of the resonator parameters.

Near‐Infrared Lasing in Four‐Zigzag Edged Nanographenes by 1D versus 2D Electronic π‐Conjugation

“…Among the different ways reported in literature for determining E th-ASE , [30] we have chosen the one based on the emission linewidth (FWHM) evolution with the pump energy density to enable comparisons to previously reported values with similar compounds, for which this method was used. [22,26] Thus, E th-ASE corresponds to the pump energy density at which the FWHM reaches the average value between the ones observed at low and high excitation density, which approximately coincides with that at which a drastic slope change in I out is seen. The obtained results are listed in Table 1.…”

“…These values are more than 40 nm red‐shifted with respect to those reported for FZ3, which displayed dual‐ASE at 685 and 739 nm. [ 26 ] These results indicate that the strategy of increasing n followed in the series reported here (AA‐Ar, TT‐Ar, and PP‐Ar) to obtain emissions at larger wavelengths is more NIR emitter efficient in terms of conjugation than that of increasing m (followed in the previous series AA‐Ar, FZ2, FZ3), as a larger red‐shift is observed with a lower increase in π‐electrons. In other words, this means that electronic delocalization is more efficient in the compounds with larger but highly asymmetrical edges (pentacene‐like versus tetracene‐like, in PP‐Ar versus FZ3, respectively) rather than in systems with larger total number of benzene rings (i.e.…”

Gain Bandwidth Engineering in Polymer Blends for Full‐Color‐Tunable Lasers

“…[15][16][17][18][19] The distinct gain bandwidth has enabled lasing in a relatively wide range of discrete wavelengths but has not led to continuous tuning in the entire emission spectrum. [20][21][22] Note that few organic gain medium exhibit dual-wavelengths amplified spontaneous emission (ASE)/lasing, [23][24][25][26][27][28] and tunable lasing between different vibronic transitions has been achieved in some organic crystals by increasing absorption intensities at specific emission bands. [29,30] This dilemma to transcend the gain bandwidth limitation still has not been broken through for most organic gain media, especially for organic amorphous semiconductor materials applied as gain media.…”

Large Polycyclic Aromatic Hydrocarbons as Graphene Quantum Dots: from Synthesis to Spectroscopy and Photonics

“…Very recently, FZ3 was demonstrated to sustain dual ASE and lasing at both 685 and 749 nm, even though the excitation threshold to achieve ASE was 10 times larger than those observed for FZ2 and FZ3. [81] This high threshold could be attributed to the spectral overlap between gain and absorption from charge-separated states in the NIR.…”