Tailoring between network rigidity and nanosecond transient absorption in a-GexAs35-xSe65 thin films

TL;DR

This study demonstrates how the rigidity of a-GexAs35-xSe65 thin films influences nanosecond transient absorption, revealing a self-trapped exciton mechanism and showing that excitation fluence can modulate TA in different network states.

Contribution

First experimental observation linking network rigidity to transient absorption in a-GexAs35-xSe65 films, highlighting the role of bond rearrangements and excitation fluence.

Findings

TA decreases dramatically with increased network rigidity.

Excitation fluence can enhance TA even in rigid networks.

TA blueshifts as mean coordination increases.

Abstract

In this letter, we report the first observation of dramatic decrease in nanosecond (ns) pulsed laser induced transient absorption (TA) in a-GexAs35-xSe65 thin films by tuning the amorphous network from floppy to rigid. Our results provide the direct experimental evidence of a self trapped exciton mechanism, where trapping of the excitons occurs through bond rearrangements. Taken together, a rigid amorphous network with more constraints than degrees of freedom, are unable to undergo any such bond rearrangements and results in weaker TA. However, we also demonstrate that excitation fluence can be effectively utilized as a simple tool to lift up enough constraints to introduce large TA even in rigid networks. Apart from this, we also show that TA is tunable with network rigidity as it blueshift when the mean coordination is increased from 2.35 to 2.6.