# A Simple Three-Step Method for the Synthesis of Submicron Gold Particles: The Influence of Laser Irradiation Duration, Pulse Energy, Laser Pulse Duration, and Initial Concentration of Nanoparticles in the Colloid

## TL;DR

This paper presents a three-step laser-based method to create submicron gold particles, showing how factors like laser settings and nanoparticle concentration affect the final size.

## Contribution

A novel three-step laser method for synthesizing submicron gold particles without chemical reagents is introduced.

## Key findings

- Submicron gold particles (50-200 nm) are formed through sequential laser irradiation steps.
- Picosecond laser pulses produce larger particles than nanosecond pulses due to surface melting.
- Higher nanoparticle concentration and laser energy increase particle size up to a fragmentation threshold.

## Abstract

This work demonstrates a three-step method for the synthesis and production of submicron spherical gold particles using laser ablation in liquid (LAL), laser-induced fragmentation in liquid (LFL), laser-induced nanochain formation, and laser melting in liquid (LML). The nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV–visible spectroscopy. In the first stage, spherical gold nanoparticles with a size of 20 nm were obtained using LAL and LFL. Subsequent irradiation of gold nanoparticle colloids with radiation at a wavelength of 532 nm leads to the formation of gold nanochains. Irradiation of nanochain colloids with radiation at a wavelength of 1064 nm leads to the formation of large spherical gold particles with a size of 50 to 200 nm. The formation of submicron gold particles upon irradiation of 2 mL of colloid occurs within the first minutes of irradiation and is complete after 480,000 laser pulses. Increasing the laser pulse energy leads to the formation of larger particles; after exceeding the threshold energy (321 mJ/cm2), fragmentation is observed. Increasing the concentration of nanoparticles in the initial colloid up to 150 μg/mL leads to a linear increase in the size of submicron nanoparticles. The use of picosecond pulses for irradiating nanochains demonstrates the formation of the largest particles (200 nm) compared to nanosecond pulses, which may be due to the effect of local surface melting. The described technique opens the possibility of synthesizing stable gold nanoparticles over a wide range of sizes, from a few to hundreds of nanometers, without the use of chemical reagents.