Dynamics of Two Distinct Exciton Populations in Methyl-Functionalized Germanane

Abstract

Methyl-substituted germanane is an emerging material that has been proposed for novel applications in optoelectronics, photoelectrocatalysis, and biosensors. It is a two-dimensional semiconductor with a strong above-gap fluorescence associated with water intercalation. Here, we use time-resolved photoluminescence spectroscopy to understand the mechanism causing this fluorescence. We show that it originates from two distinct exciton populations. Both populations recombine exponentially, accompanied by the thermally activated transfer of exciton population from the shorter- to the longer-lived type. The two exciton populations involve different electronic levels and couple to different phonons. The longer-lived type of exciton migrates within the disordered energy landscape of localized recombination centers. These outcomes shed light on the fundamental optical and electronic properties of functionalized germanane, enabling the groundwork for future applications in optoelectronics, light harvesting, and sensing.

2D Functionalized Germananes: Synthesis and Applications

“…Notably, the resulting GeMe possesses an optical bandgap of 1.7 eV (0.1 eV larger than GeH), with enhanced thermal stability up to 250 °C (75 °C for GeH), [55] and, most interestingly, significantly improved the photoluminescence properties (Figure 3c) that could find broad potential in many applications. [55,92,96] When GeMe was heated above 250 °C, a decrease in photoluminescence emission and small shift in the onset of diffuse reflectance was observed. A huge mass loss at 300 °C that corresponded to 90% of CH 3 groups was observed by thermogravimetric analysis.…”

“…[97] Studies by time-resolved photoluminescence spectroscopy at different temperatures prove that the fluorescence is originated from two distinct populations of emitting excitons localized at recombination centers within the intercalated water. [96] Other Functionalized Germananes (Other Covalent Groups, R Termination): The initial success of functionalized germananes, GeH and GeMe, by the "top-down" approach evidences their tunable properties by tailoring the ligand identity and coverage of the 2D germanane framework. This motivates [63] Copyright 2019, American Chemical Society.…”

“…The vital role of H 2 O in deintercalation reactions is reflected in the strong‐above gap fluorescence properties of GeMe. [ 96 ] As opposed to GeH, the GeMe reversibly absorbs water in the vdWs space and shows near negligible photoluminescence. [ 97 ] Studies by time‐resolved photoluminescence spectroscopy at different temperatures prove that the fluorescence is originated from two distinct populations of emitting excitons localized at recombination centers within the intercalated water.…”

“…[ 97 ] Studies by time‐resolved photoluminescence spectroscopy at different temperatures prove that the fluorescence is originated from two distinct populations of emitting excitons localized at recombination centers within the intercalated water. [ 96 ]…”

Multi‐Sensing Platform Based on 2D Monoelement Germanane

“…CH 3 Ge also demonstrates outstanding band‐edge fluorescence and photoluminescence (PL) properties. [ 26–28 ] Therefore, CH 3 Ge has been documented as a fluorescent marker on a microrobot system for drug delivery. [ 29 ] On the other hand, the PL of CH 3 Ge is highly associated with the absorption of water molecules in its interlayer space.…”