Astronomers have extensively studied the ERE of the Red Rectangle (RR) Nebula in the Milky Way for nearly a century. ERE stands for extended red emission. The ERE from the RR is depicted in the thumbnail. Today, controversy surrounds the mechanism by which the ERE is produced. Two competing mechanisms: PL and BB radiation have emerged, both of which rely on the UV emission from a pair of stars in the RR Nebula:. PL stands for photoluminescence and BB for blackbody.
In PL experiments on Earth, solid samples are irradiated with continuous wave laser light. Measured PL spectra show the laser light is redshift to longer wavelengths, e.g., PL could produce red photons at a wavelength of 0.62 microns from a hypothetical UV laser having Planck energy 10.5 eV (wavelength 0.118 microns). PL requires a number of bunched UV photons because the conversion efficiency from UV to red light is always < 100%. Nevertheless, PL in cosmic dust is proposed  as the ERE mechanism excited by > 10.5 eV UV photons.
However, cosmic dust in the interstellar medium (ISM) comprised of discrete nanoparticles (NPs) separated by large distances differs significantly from the solid samples in Earth-bound PL experiments. In the ISM, PL may only occur by the absorption of a single UV photon in a NP. Since the PL conversion efficiency < 100%, it may be safely concluded PL from single UV photon absorptions in cosmic dust is not the ERE mechanism.
Since PL in cosmic dust is highly unlikely, PL as the source of ERE has been proposed  supplemented by thermal BB radiation. The stars in the RR Nebula have temperatures of about 7000 K that by Wien’s law limits the BB emission peak to about 0.41 microns or 3 eV, and therefore it can be concluded that BB radiation cannot produce UV photons having Planck energy > 10.5 eV necessary to explain the ERE in the RR.
Instead of PL and BB radiation, carbon molecules having < 28 atoms are assumed  heated to temperatures in excess of 1500 K by absorption of a single UV photon. In support of this assumption, laser heating experiments  of soot comprising 30-100 nm carbon NPs deposited on the aluminum foil vanes of a Crookes radiometer are presented. Laser irradiation of the soot film produces an emission spectrum (Fig. 2(a) of ) that peaks at about 620 nm. Temperatures were estimated and not measured. Fits of BB radiation alone did not approximate the measured spectrum. Mie theory does indeed give a reasonable estimate of the efficiency of NP absorption of laser radiation provided the NPs are not in contact with each other as in the soot film, but as a first approximation is reasonable. Indeed, Mie theory gave a better approximation to the spectral shape at a temperature of 3800 K.
The Mie theory estimate of 3800 K necessary to fit the measured spectrum cannot be correct as the aluminum foil having a melting point of about 960 K would have been exceeded, but foil damage was not reported. Whatever caused the emission spectrum did not require high temperatures consistent with Planck’s theory of BB radiation.
Classical Physics v Quantum Mechanics
Classically, NPs conserve absorbed EM energy of any form by an increase in temperature that in turn is emitted as VIS and IR radiation, but QM differs. EM stands for electromagnetic and QM for quantum mechanics. Because of the high surface to volume ratio of NPs, the absorbed EM energy in the form of VIS – UV light concentrates in the NP surface, and therefore the NP is placed under TIR confinement. TIR stands for total internal reflection. By QM, the TIR confinement requires the heat capacity of the atom to vanish, and therefore the absorbed VIS-UV light cannot be conserved by an increase in NP temperature. Depending on the diameter of the NP, QED creates photons inside the NP that may be blue or redshift relative to the absorbed VIS-UV radiation. Blue shift requires multi-photon absorption by laser irradiation as in Earth bound experiments;
In the ISM, the redshift Z = (Lo – L)/L, where Lo and L are the wavelengths of the QED and absorbed VIS-UV photons. Here, Lo = 2 nD, where n and D are the refractive index and diameter of the NP, e.g., see http://www.nanoqed.org, “Cosmology by Cosmic Dust – Update,” 2010.
Crookes Radiometer Experiment
The Crookes radiometer experiment  provides an excellent example of QED induced radiation. Mie theory gives the efficiency of absorption of laser radiation by the individual carbon NP, but not the emission. Moreover, the NPs in the soot film are not isolated from each other, and therefore the effective NP diameter increases above that for 30-100 nm NPs. If the NPs are isolated, no temperature increase is expected by QM. But if the laser photons are absorbed in the aluminum foil, thermal energy is transferred to the NPs in contact wuth the foil, and therefore QED enhances the VIS emission above that given by the absorption of laser light by Mie theory. Regardless, the temperature increase if any should be minimal and < 960 K - certainly not 3800 K.
Unlike the carbon NPs in the film deposited on the Crookes radiometer vanes, NPs in the ISM are indeed isolated from each other. By QM, absorption of a single > 10.5 eV UV photon does not increase the NP temperature, but instead is redshift by QED toward the red VIS and the NIR. In the ISM, NP diameters vary from 0.01 to 0.5 microns. For silicate NPs having n = 1.45 and diameter D = 0.214 microns, the QED photons created have wavelength Lo = 0.62 microns. By QED, the single 10.5 eV UV photon having L = 0.118 microns therefore creates a red photon by a redshift Z ~ 4.3 comparable to that of Supernovae explosions. If the redshift Z is interpreted as a Doppler effect as in the Hubble law, the RR is moving away from the Earth at almost the speed of light, but this is an absurdity as the RR is in our own Milky Way galaxy.
1. Both PL and BB radiation including variants thereof may be safely dismissed as mechanisms for the ERE.
2. QED induced radiation asserts the VIS and NIR in the ISM are caused by the absorption of UV radiation in cosmic dust NPs. In the ISM, mid and far IR spectra may also be explained by QED induced redshift, but requires larger cosmic dust particles.
3. The redshift measurements of Supernovae explosions have nothing to do with an expanding Universe, but rather cosmic dust. The RR color by QED induced redshift radiation clearly shows that high Z redshifts need not be limited to distant Supernovae and is natural in the colors we see in the Milky Way.
5. The Crookes radiometer experiment offers an excellent opportunity to confirm the QM prediction that the measured spectrum is produced without any significant change in temperature, say by applying the carbon NP soot to combustible paper vanes.
 A. N. Witt, et al., The Excitation of Extended Red Emission: New Constraints on Its Carrier from Hubble Space Telescope Observations of NGC 7023,* ApJ, 636, 303 (2006)
 W. W. Duley, Excitation of extended red emission and near-infrared continuum radiation in the interstellar medium, ApJ, 705, 446 (2009). See
 S. Wang, et al., Electromagnetic excitation of nano-carbon in vacuum, Optics Express, 13, 3625 (2005). See