2023-12-31 21:00:00
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There is no doubt that fireworks are one of the most fascinating phenomena to see in the night skies. Usually projected during festive times, these colorful rockets paint the sky with multicolored sparkles, dazzling everyone who looks at them with their bright reds, dark greens or sparkling golds.
However, among that exuberant palette of colors, there is one that is always conspicuous by its absence: the blue. The explanation for this intriguing lack is directly related to the chemistry that encompasses fireworks displays.
THE CHEMISTRY OF FIREWORKS
Have you ever wondered what the science is behind the acclaimed fireworks? Well, the phenomenon begins with the choice of the components that will be contained within the pyrotechnic element, that is, what will be the chemical compounds which, when subjected to high temperature, will emit energy in the form of light and shine in the sky. Commonly, the most used elements will be the metallic saltssince each one has the capacity to emit photons at different frequencies, which translates into a wide range of colors when subjected to thermal excitation.
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Thus, when a firework is lit and rises into the sky, the mixture of explosive dust heats up, so that all the atoms that make up each substance they get excited and they vibrate strongly. It is at that moment of maximum excitation when the electrons found in the outermost parts of the atom absorb that great temperature in the form of energy, which allows them jump to higher orbits. However, it is a very unstable state, so just a few nanoseconds After being excited, they return to their normal, equilibrium position, releasing energy again in the form of visible light.
Now, the excitation has been so high that the release of energy, even if it is in the form of light, also has great power: the color explosion that we see from our location on the ground. Now, the color that is emitted depends directly on the energy jump of each electron, which is defined by each type of compound. Thus, if there are sodium salts in the mixture, the jumps create a yellow color, if there are strontium salts, they produce a red color, if those introduced into the rocket are aluminum salts, the tones of the fires will be gray, while if, on the contrary, they are barium salts, the tones of the explosions will be green.
THE IMPOSSIBLE BLUE
But what happens then with blue? Well, we must keep in mind that the colors we see are due to the fact that electrons emit energy in the form of light, that is, photons and, depending on the frequency and wavelength at which they move, they will be appreciable one or other colors according to the visible light spectrum: the lowest frequencies will belong to red tones, while the highest ones will belong to bluish colors.
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Visible light spectrum. Red, on the right, is identified with the longest wavelength and lowest frequency; while blue is identified with a shorter wavelength and higher frequency.
However, the problem lies in the difficulty of finding elements that emit light in high frequencies that give rise to bright and bright blues. And, to excite the electrons of those elements that could provide the blue color, a considerably higher energy, compared to other colors, which would require higher temperatures and, consequently, greater energy consumption. Furthermore, in most elements, there is not a single jump, but rather they are severalso that, when the resulting colors are combined, there are usually “brighter” ones that eclipse the blues, making their appearance almost impossible.
Historically, the copper has been the main candidate in the search for the blue tone. However, due to its composition, with the de-excitation of its electrons, green light would also be emitted, which covers the limited blue, not allowing it to reach the necessary visual intensity. On the other hand, over the years, many other metals have been considered as potential favorites to achieve blue, such as lithium or cobalt, but blue emission remains a considerable technical challenge.
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