As a rule, everything around you glows – in other words, it emits photons. Some infrared ones, some visible ones, some ultraviolet (or even higher-frequency) ones. How much of each depends on the temperature of the material. Most things (e.g. you) are too cold to be visibly glowing, but they still emit plenty of infrared radiation.

Now, standard solar cells convert visible photons into electricity. Any incoming infrared photons, however, aren't strong enough to kick any electrons loose, so they go to waste. Here, the researchers used carbon nanotubes to absorb the wasted infrared photons. This heats up the nanotubes, which then emit visible photons, which then increase electricity generation.

There is no way to convert heat to electricity directly, unfortunately. However, you can get small amounts of electricity out of temperature differences: https://en.wikipedia.org/wiki/Thermoelectric_effect

Well, if you have enough heat, you can boil water and then use the steam to turn a turbine... I suppose in some sense this is dependent on a temperature difference, but I wouldn't call the amount of electricity we get by this method 'small.'

It is absolutely dependent on a temperature difference, because it relies on cooler water that isn't already flashing into steam.

Once a solar cell is built with this technology, do you think there will be enough light emitted by the nanotubes to make the solar panels appear to glow, themselves? Because that would be pretty interesting.

> Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect Naik called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one.

So, from a pragmatic perspective, I would say that no, they wouldn't glow - proper engineering would ensure these particles are collected.

I'm a bit skeptical that that would work. Otherwise you could build a perpetual motion machine by having the nanotubes in a hot room and running your perpetual motor off a solar cell powered by the light.

My guess is when the article says emit light they mean emit infra red light / radiation rather than visible. The article doesn't really make sense to me - I imagine someone got confused by the physics rather than it being an actual breakthrough in energy generation. I note the article says "propose a way to build" rather than having actually built something that works.

Critically these photons are not heating up the material. It’s like saying photons reflecting off a mirror heat it. No, the photons that are not reflected do heat the mirror, but not the reflected ones. (At least mostly.)

Light with a short enough wavelength (UV-B, for example) has enough energy to damage the DNA in our skin and increase our risk of skin cancer.

I don't know why they're calling that "light". It's not clear to me if it means visible light. The paper seems to imply that it peaks in the near-infrared. They appear to be using "light" in the general sense of "photons"... but it's all photons.

They're talking about very high temperatures, the kind that emit significant visible light as well.

The exact details depend on the chemical composition of the material, but for a simple model, check out https://en.wikipedia.org/wiki/Black-body_radiation

All physical objects emit electromagnetic radiation corresponding to their temperature (as opposed to reflected, reaction-induced, or stimulated radiation, more below), with a corresponding blackbody radiation curve. Note that blackbody emissions don't have a specific frequency (say, unlike laser light), though the curve has a peak emission.

Traditional incandescent light bulbs are blackbody emitters, as is a hot coal, the Sun and other stars, or the glowing elements of an electric radiant heater. Human eyes see blackbody radiation, in the visible range, as having a characteristic colour, which paradoxically gets bluer as the temperature gets higher, so the ruddy tones of low-voltage incandescent lamps are low colour temperature, and the intense white of halogen lamps are high colour temperatures. Blackbody radiation and colour temperatures are given in Kelvin, with typical visible light corresponding roughly to ~3,000 - 8,000K. You might also recognise these values from gamma or colour correction values on monitors and video equipment.

(Colour temperatures were used to judge processing for ceramics and metal processing / firing / smelting processes as well. They're also used to classify stellar temperatures, and in conjunction with brightness and/or distance estimates can be used to find stellar sizes.)

Infrared light is characteristic of peak blackbody emissions of bodies at or near "room temperature". So IR is not heat, but is associated with hot objects. Heat itself is ... thermal energy, which is its own complex thing.

Since all EMR carries energy, all EMR heats objects in which it is absorbed. A sufficiently intense emission above the IR range will also heat an object. However hot objects in near proximity transfer a great deal of thermal energy directly as IR emissions. The illuminating capability of "white" light (typical solar emissions) allows a small amout of EMR energy to provide a high degree of visual information without imparting much heat on the illuminated objects (though it does impart some). Consider that even an (inefficient) 100W incandescent bulb, whilst hot to the touch, does not significantly heat the objects it is illuminating, and a far more efficient equivalent LED lamp, drawing about 15W of electrical power, accomplishes the same illuminating power with vastly less heat. We don't have to toast things to be able to see them, just bounce a small amount of (high-energy) visible light off of them.

Not all light (or more accurately, EMR) is blackbody radiation. There can be chemically-emitted light, directly from chemical reactions. The blue glow of methane (natural gas) combustion is a chemical emission, contrasted with the yellow-white glow of a candle, actually blackbody emissions of suspended soot particles in the smoke plume. (There's a blue region of chemical emission at the base of the flame.)

Chemical emissions are based on specific frequencies of EMR emitted as electrons transition between energy states, if I understand correctly are a quantum phenomenon. Fluourescent and LED lamps also work based on chemical / valance emissions, and operate in far narrower bands than blackbody emissions -- one of the reasons these lamps can appear harsher than incandescents. Similarly various chemical lamps, especially high- or low-pressure sodium vapour, formerly popular as street lighting, which emit in narrow bands (low-pressure especially).

Some forms of ionizing radiation are also EMR emissions, at far higher energy levels, triggered by nuclear rather than electron emissions. Typically gamma-rays.

And stimulated emissions such as lasers and masers are ... another phenomenon I understand only poorly, but are also tuned to very tight frequencies. Radio and microwave emitters are somewhat similar.

https://en.wikipedia.org/wiki/Black-body_radiation

https://en.wikipedia.org/wiki/Infrared

https://en.wikipedia.org/wiki/Heat