It is true that when you ignite a metal nanoparticle, you will get light, usually another color, but the reason remains to be discussed. In a new article published in Nano Express, a journal of American Chemical Society, Stephen Link, a chemist at Rice University, and Cai, a graduate student, put forward the view that it is photoluminescence rather than Raman scattering that makes gold nanoparticles have remarkable luminescent characteristics. Researchers say that understanding how and why nanoparticles emit light is very important for improving the efficiency of solar cells and designing particles that use light to trigger or sense biochemical reactions. For a long time, scientists have been arguing about how one color of light makes some nanoparticles emit different colors of light. Cai, the first author of the paper, said that this debate originated from semiconductor research in the 1970s and recently extended to the field of plasma structure.

Boko Park-Popular Science: Raman effect is like a ball bouncing back after hitting an object, but in photoluminescence, the object absorbs light, and the energy in the particle moves around and then emits it. Eight years ago, Link's research group reported the first spectral study on the luminescence of a single plasma nanorod, and this new paper was published on the basis of this study. This study shows that when hot carriers (electrons and holes in conductive metals) are excited by CW laser energy, when they relax, they recombine with photons released by interaction, which will produce this luminescence. By irradiating a gold nanorod with a laser with a specific frequency, researchers can feel the temperature, which can only come from excited electrons. This is a sign of photoluminescence, because Raman theory assumes that phonons, not excited electrons, are responsible for light emission.

Link and Cai said: Compared with Stokes radiation, the efficiency of anti-Stokes radiation has been proved. When the energy output of particles is greater than the input, anti-stokes emission will occur, and when the energy output of particles is greater than the input, anti-stokes emission will occur. Stokes and anti-Stokes measurements were once considered as background effects related to surface enhanced Raman scattering. The results show that these measurement results provide very important and useful information for researchers. Metal nanoparticles such as silver and aluminum are also plasmons, and Cai hopes to determine their Stokes and anti-Stokes properties by testing. But first, we will study how photoluminescence decays with time. The direction of the research team is to measure the lifetime of this radiation, that is, how long it can survive after the laser is turned off.

Researchers at Rice University are studying the light source emitted by plasma metal nanoparticles. In a new paper, they think that photoluminescence has advantages over Raman scattering. From left: Cai Yuyi, Benaz Josto Waal and Lawrence Tauzin. Photo: Jeff Fitlo/Rice University

Boko Park-Popular Science | Research/From: Rice University

David Ruth, Rice University

Reference periodical literature: Nano Express

DOI: 10. 102 1/ACS . nano lett . 8b 04359

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