Sorry for a potentially stupid question: why do they need to convert heat into visible light? Why can't we convert heat directly into electricity at the same time as we convert visible light into electricity?
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
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.
So, from a pragmatic perspective, I would say that no, they wouldn't glow - proper engineering would ensure these particles are collected.
> 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.
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'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.)
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.
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.