Gases are often perceived as invisible, a common perception shaped by the clear air around us. However, under specific conditions, certain gases can emit light and display vibrant colors. While many remain colorless, some energized gases, like neon, can exhibit distinct hues, including shades of pink. This phenomenon involves intricate atomic interactions, revealing how energy translates into visible light.
How Gases Get Their Color: The Basics of Emission
A gas produces visible light and color through fundamental atomic processes. When energy, such as an electrical current, excites electrons within gas atoms, they jump to higher energy levels. These excited electrons quickly return to their original, lower energy levels, releasing absorbed energy as photons.
The color of the emitted light depends on the specific energy released, which corresponds to a particular wavelength on the electromagnetic spectrum. Each element possesses a unique set of electron energy levels, meaning that each type of gas emits a distinctive pattern of wavelengths, known as its atomic emission spectrum. This unique spectral “fingerprint” determines the characteristic color we observe from an energized gas.
The Primary Pink Gas: Neon and Its Relatives
When considering “pink gas,” neon often comes to mind, although pure neon gas typically glows a distinct reddish-orange when electrified. This characteristic reddish-orange hue is due to numerous emission lines in that range of the spectrum. However, neon can appear pink under certain conditions, especially when mixed with other noble gases or viewed through specific filters. For instance, a mixture of neon (95%) and xenon (5%) can produce pink and blue light in plasma lamps.
The exact color emitted by a gas in discharge tubes is influenced by the gas mixture and pressure. Argon gas, for example, emits a lavender or light purple hue on its own, but when combined with mercury, it can create vibrant blue, green, yellow, or white colors. Even pure neon can produce a paler red or pink if the tube contains higher levels of the gas. Beyond neon, hydrogen gas also presents a pinkish-purple glow in discharge tubes under specific conditions. While hydrogen-alpha emission is a deep red, the overall appearance of hydrogen gas in a discharge tube can be blue-violet or even pink-orange.
Other Instances of Pink Gas Phenomena
Pink hues in gases extend beyond specialized lamps to natural atmospheric phenomena. The Aurora Borealis, or Northern Lights, can display pinks and reds, especially when excited nitrogen and oxygen atoms in the atmosphere emit light at lower altitudes. Nitrogen molecules at around 100 km can produce pink and dark red fringes in the lower edge of an aurora. The combination of different amounts of gases, particularly nitrogen and oxygen, contributes to the purple and pink lights seen in these displays.
Specialized gas discharge tubes and plasma lamps also showcase various gases producing pinkish glows. In these devices, various gases, including nitrogen, hydrogen, and even water vapor, can generate pink or reddish-purple light. For example, hydrogen plasma is described as pink or reddish, and air plasma can appear intensely pink or purple.
Beyond True Gas Color: Misconceptions and Context
Not every instance of a pink appearance involves a gas intrinsically emitting pink light. For example, pink smoke is typically caused by colored particulate matter suspended in the air, not by the gas itself having a pink color. Such smoke can arise from the burning of substances like iodine, which produces a pink plume.
Another common misconception relates to the use of colored filters. A colorless gas might appear pink if viewed through a pink or red filter. These filters work by absorbing certain wavelengths of light while allowing others, such as red or pink, to pass through, thus coloring the light that reaches the eye.