Brilliant fluorescent properties of Na2S(x) obtained from Na2SO3 or Na2S2O3

Question

When $\ce{K2SO3}$ or $\ce{Na2SO3}$ is heated strongly by any method (in a flame, in an electric arc, on a metal plate in an induction heater), the resulting residue should be a mixture of $\ce{Na2SO4/K2SO4}$ and $\ce{Na2S}$ or $\ce{K2S}$. (Indeed, when treated with water, the smell of hydrogen sulfide is heard, and with copper sulfate a black precipitate is formed). The hugely intense orange fluorescence of this residue in ultraviolet rays of $\pu{365 nm}$ is interesting me:

• Does ordinary sodium sulfide (which is not yet available to me in its pure form) have very strong fluorescent properties?

Or, during the heating of sulfite, sodium polysulfides are also formed, even despite the oxidizing atmosphere? However, there is also no particular information about the intense fluorescence of alkali metal polysulfides.

The same fluorescence in UV appears after strong heating of thiosulfate, $\ce{Na2S2O3}$, in ambient air (but at least it is known for certain that polysulfides of the $\ce{Na2S5}$ type are formed in the residue).

PS. Any such fluorescence disappears completely after treatment with water... even after the water evaporates.

Answer 1

You have managed to run a plethora of uncontrolled reactions with very interesting results. But, as jimchmst correctly put in comment section, more research, analysis, and precise data collection are needed before drawing any conclusions to your findings. Yet, I'd suggest that the brilliant fluorescent properties shown in some crystals (not all of them) should be due to crystal rearrangement of molecules upon high temperature heating. Disappearance of fluorescent properties due to addition of water may suggest that change og crystal structure by dissolving the crystals and back to normal crystal when water evaporated.

I suggested this phenomenon according to the similar research presented in Ref.1, abstract of which states:

“Glow-in-the-dark” materials are known to practically everyone who has ever traveled by airplane or cruise ship, since they are commonly used for self-lit emergency exit signs. The green afterglow, persistent luminescence (PeL), is obtained from divalent europium doped to a synthetic strontium aluminate, but there are also some natural minerals capable of afterglow. One such mineral is hackmanite, the afterglow of which has never been thoroughly investigated, even if its synthetic versions can compete with some of the best commercially available synthetic PeL materials. Here we combine experimental and computational data to show that the white PeL of natural hackmanite is generated and controlled by a very delicate interplay between the natural impurities present. The results obtained shed light on the PeL phenomenon itself thus giving insight into improving the performance of synthetic materials.

The photos of the samples used in their study under white light, $365, 302,$ and $\pu{254 nm}$ together with their persistent luminescence are shown in following figure:

At least two samples (Greenland and Koksha Valley 1) show fluorescent properties under UV light $(\pu{365 nm})$ similar to yours. This phenomena is explained by Ref.1 as the electron transition between one center $(\ce{S2^2-})$ to another vacant site, for example in this case, chlorine vacancy $(V_\ce{Cl})$.

I think it'd be a good idea to separate the crystals from the parts of your sample that is displaying fluorescent properties and studied them according to the studies have been done in Ref. 1 including crystallographic studies. Also, same should be done to other parts, which do not show fluorescent properties for comparison.

I also asked you a question regarding any organic matter involved in your experiment (may be as an impurity), but your response was no. The reason I it was because it may change the crystal structure of the material if there is one. If you look at the paper you provide in your response (Ref.2), you see when the author prepare the test sample with use of acetone it shows fluorescent properties, but no such properties without use of acetone. My question is based on properties shown in Ref.3 (for your information), which shows the importance of crystal structure on this phenomenon.

There is also another reference you may look at in this study, Re.4, which discusses a variety of phase transitions of $\ce{Na2SO4}$ between its five anhydrous polymorphs with increasing temperature.

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References:

1. Cecilia Agamah, Sami Vuori, Pauline Colinet, Isabella Norrbo, José Miranda de Carvalho, Liana Key Okada Nakamura, Joachim Lindblom, Ludo van Goethem, Axel Emmermann, Timo Saarinen, Tero Laihinen, Eero Laakkonen, Johan Lindén, Jari Konu, Henk Vrielinck, David Van der Heggen, Philippe F. Smet, Tangui Le Bahers, and Mika Lastusaari, "Hackmanite—The Natural Glow-in-the-Dark Material," Chem. Mater. 2020, 32(20), 8895–8905 (https://doi.org/10.1021/acs.chemmater.0c02554).
2. Russell D. Kirk, "The luminescence and tenebrescence of natural and synthetic sodalite," American Mineralogist 1955, 40(1-2), 22–31 (https://rruff.info/doclib/am/vol40/AM40_22.pdf).
3. Yunsu Ma, Yongjie Liu, Yuan Wang, Fan Zhang, and Dongzhi Yang, "A novel sodium-fluorescent crystal," Royal Society Open Science 2021, 8(3), Article ID 201987 (10 pages) (https://doi.org/10.1098/rsos.201987).
4. Y. S. Vidya and B. N. Lakshminarasappa, "Preparation, Characterization, and Luminescence Properties of Orthorhombic Sodium Sulphate," Physics Research International 2013, 2013, Article ID 641631 (7 pages) (https://doi.org/10.1155/2013/641631).