• Subsequent detailed studies of concentration and speed of cooling behavior of Shpolskii systems by L. A. Nakhimovsky and coauthors led to a hypothesis that these systems are
  metastable segregational solid solutions formed when one or more chromophores replace two or more molecules in the host crystalline lattice.

• The original observation of the Shpolskii effect was made at liquid nitrogen temperature (77 kelvins), but using temperatures close to that of liquid helium (4.2 K) yields
  much sharper spectral lines and is the usual practice.

• Shpolskii systems are low-temperature host–guest systems – they are typically rapidly frozen solutions of polycyclic aromatic hydrocarbons in suitable low molecular weight
  normal alkanes.

• The narrow lines characteristic of the Shpolskii systems are only observed at cryogenic temperatures because at higher temperatures many phonons are active in the lattice
  and all of the amplitude of the transition shifts to the broad phonon sideband.

• In addition to the weak inhomogeneous broadening of the transitions, the quasi-lines observed at very low temperatures are phonon-less transitions.

• The emission and absorption spectra of lowest energy electronic transitions in the Shpolskii systems exhibit narrow lines instead of the inhomogeneously broadened features
  normally associated with spectra of chromophores in liquids and amorphous solids.

 

Works Cited

[‘1. E. V. Shpolskii, A. A. Ilina and L. A. Klimova, 1952, Transactions Doklady of the U.S.S.R. Academy of Sciences, volume 87, page 935
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Soviet Physics Uspekhi. IOP Publishing. 3 (3): 372–389. doi:10.1070/pu1960v003n03abeh003277. ISSN 0038-5670.
3. ^ Shpol’skiĭ, É V (31 March 1962). “Problems of the Origin and Structure of the Quasilinear Spectra of Organic Compounds at Low Temperatures”.
Soviet Physics Uspekhi. IOP Publishing. 5 (3): 522–531. doi:10.1070/pu1962v005n03abeh003436. ISSN 0038-5670.
4. ^ Shpol’skiĭ, É V (31 March 1963). “New Data on the Nature of the Quasilinear Spectra of Organic Compounds”. Soviet Physics Uspekhi.
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5. ^ Ustyugova, L. N.; Nakhimovskaya, L. A. (1968). “Effect of crystallization conditions on absorption and fluorescence spectra of n-paraffin solutions of some
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6. ^ L. A. Nakhimovsky, M. Lamotte, J. Joussot-dubien, Handbook
of Low Temperature Electronic Spectra of Polycyclic Aromatic Hydrocarbons, Chapter II, Elsevier, 1989
7. ^ Nakhimovskaya, L. A.; Mishina, L. A.; Kleshchev, G. V. (1971). “Change of absorption spectra with isothermal aging time of rapidly frozen
solutions of diphenylene oxide in heptane”. Journal of Structural Chemistry. Springer Nature. 11 (5): 853–855. doi:10.1007/bf00743395. ISSN 0022-4766. S2CID 97368004.
8. ^ Richards, John L.; Rice, Stuart A. (1971). “Study of Impurity–Host Coupling
in Shpolskii Matrices”. The Journal of Chemical Physics. AIP Publishing. 54 (5): 2014–2023. Bibcode:1971JChPh..54.2014R. doi:10.1063/1.1675132. ISSN 0021-9606.
9. ^ Friedrich, Josef; Haarer, Dietrich (1984). “Photochemical Hole Burning: A Spectroscopic
Study of Relaxation Processes in Polymers and Glasses”. Angewandte Chemie International Edition in English. Wiley. 23 (2): 113–140. doi:10.1002/anie.198401131. ISSN 0570-0833.
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