Gold owes its 'glow' and luminescence to the quantum realm

For centuries, the glow of gold’s luminescence — the process by which materials emit light after exposure — has fascinated scientists.

Traditionally linked to semiconductors like silicon, luminescence aids scientists in understanding vital electronic processes, especially in devices like solar cells.

However, researchers recently achieved a breakthrough that has clarified the behavior of metals under luminescence, which had long remained a mystery.

Cracking the code to gold’s luminescence

Metals have been known to emit light since 1969, but understanding their luminescence has eluded scientists for decades. Consequently, this mystery persisted due to the complex quantum mechanical effects that govern luminescence at the nanoscale.

The breakthrough came from Giulia Tagliabue’s team at the Laboratory of Nanoscience for Energy Technologies (LNET), within a prestigious School of Engineering.

They developed high-quality monocrystalline gold films, ranging from 13 to 113 nanometers thick. These films were key to eliminating the confounding factors that had obscured earlier experiments.

Laser beams reveal gold’s luminescence

Using focused laser beams, the researchers observed a faint glow from these gold films. This unexpected and detailed data prompted collaboration with theoreticians from the Barcelona Institute of Science and Technology (BIST), the University of Southern Denmark, and the Rensselaer Polytechnic Institute in the USA.

Together, they applied refined quantum mechanical models to interpret the results. Subsequently, this collaborative effort resulted in the first complete and quantitative model of photoluminescence in gold.

This model defines how electrons and their counterparts, known as holes, respond to light in a specific way unique to photoluminescence.

Surprising quantum effects

As the team investigated further, they found unusual quantum effects in unexpectedly thick gold films.

“We observed certain quantum mechanical effects emerging in films of up to about 40 nanometers, which was unexpected. “Normally for a metal, you don’t see such effects until you go well below 10 nm,” Tagliabue clarified.

This finding is crucial because it pinpoints exactly where luminescence occurs in the gold, which is essential for using it as a probe in scientific research.

Additionally, the researchers discovered a new use for the gold’s photoluminescent signal. It can measure surface temperatures at the nanoscale, offering a significant benefit due to the difficulties associated with temperature measurements in such small scales.

Tackling climate change with new technologies

The implications of this research extend far beyond basic science. “To combat climate change, we are going to need technologies to convert CO2 into other useful chemicals one way or another,” stated Alan Bowman, a postdoctoral researcher at LNET and the study’s first author.

Gold and copper, which the team will explore next, are vital for triggering chemical reactions that produce solar fuels.

These fuels convert solar energy into chemical bonds, offering a sustainable energy storage solution. Improved understanding of metal surfaces through luminescence could enhance the efficiency of these reactions.

Understanding gold’s glow and metal luminescence

In summary, the LNET team’s fascinating research has settled the long-standing debate surrounding metal luminescence and gold’s “glow” while unlocking new possibilities for nanoscale temperature mapping and energy research.

By developing high-quality metal gold films and applying innovative quantum mechanical modeling methods, the researchers have unveiled unexpected quantum effects and demonstrated the potential of photoluminescence as a self-probing tool for surface temperature.

As the world faces the urgent challenge of climate change, these findings pave the way for more efficient and effective technologies to convert CO2 into valuable chemicals, offering hope for a more sustainable future.

The LNET team’s work marks the beginning of a new era in understanding metal luminescence and its far-reaching implications for energy research and beyond.

The full study was published in the journal Light Science & Applications.

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