Why is fluorescence microscopy more commonly used in biological and polymer specimens than in metals and ceramics?
Fluorescence being a form of luminescence ("cold-body radiation"), one needs an energy gap between the ground state and the first excited state of the system in order have fluorescence following excitation of the electrons in the system. This rules out metals in which there is no energy gap and the excited electrons de-excite through excitation of acoustic phonons, amounting to heating up the lattice, to cool down by the process of heat transfer to the heat bath it is in contact with.
http://en.wikipedia.org/wiki/Fluorescence
http://en.wikipedia.org/wiki/Luminescence
Because in metals analysis is processed metal powders acids to be converted into a liquid state, causing the loss of some of their components and lead to a lack of accuracy of the results, unlike polymers and ceramics.
As Behnam Farid for bulk (or quasi-bulk) metals.
However, quantum confinement effects[1,2] in nanosize (artificial) "metals", might, not only, permit[3] fluorescence modes in nano-metals, but, it might even, paradoxically, enhanced[4,5] fluorescence (synergy).
Metal-enhanced fluorescence (MEF) seems as a promising strategy to amplify[5] the signal and significantly improve the potential of fluorescence based technology in bio-applications.
1. Quantum confinement effect - an overview http://shodhganga.inflibnet.ac.in/bitstream/10603/23484/3/03.chapter%201.pdf
2. Quantum Confinement Effects in Materials Chemistry
https://courses.washington.edu/overney/NME498_Material/NME498_Lectures/Lecture12_Reid_Quantum_Confinement.pdf
3. Gold Quantum Dots: Fluorescing "Artificial Atoms" Could Have Applications in Biological Labeling, Nanoscale Optoelectron https://phys.org/news/2004-08-gold-quantum-dots-fluorescing-artificial.html
4. A Segregated, Partially Oxidized, and Compact Ag10 Cluster within an Encapsulating DNA Host https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6118400/
5 Metal-Enhanced Fluorescence of Gold Nanoparticle and Quantum Dot Incorporated Silica Nanoparticle Aggregates [2015_Saravanan_Ramasamy_Dissertation.pdf]
https://shareok.org/handle/11244/14585
Ioannis Samaras : Just a brief remark: metallicity is a property of extended systems - in principle, macroscopic systems. Therefore, my earlier comment is not in conflict with your remarks in the second and further paragraphs of your above comment.
No, not any, conflict; it was, just, a, systems' size (scaling), contrast, by passing from bulk (extended) metallic systems, drowning all (im)possible fluorescence modes, to nano-metals' fluorescence (bring to light, possible) modes[1].
1. because they are drowning (do not favor) the previous (bulk, lower energy) modes.
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