When you light up a metal nanoparticle, you get light back. It's often a different color. That's a fact – but the why is up for debate. In a new paper, National Science Foundation-funded researchers make a case that photoluminescence, rather than Raman scattering, gives gold nanoparticles their remarkable light-emitting properties. The researchers say understanding how and why nanoparticles emit light is important for improving solar-cell efficiency and designing particles that use light to trigger or sense biochemical reactions. The longstanding debate, with determined scientists on either side, is about how light of one color causes some nanoparticles to emit light of a different color. The debate arose out of semiconductor research in the 1970s and was more recently extended to the field of plasmonic structures. By shining specific frequencies of laser light onto gold nanorods, the researchers were able to sense temperatures they said could only come from excited electrons. That's an indication of photoluminescence, because the Raman view assumes that the equilibrated temperature of phonons, not excited electrons, are responsible for light emission.
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