Luminescence
Luminescence
Assistant Professor-Dr- Muthanna Mohammed Sarhan-Department of Chemstry
muth_1974na@uoanbar.edu.iq
The electron in the molecule can move to a higher energy level through the absorption of visible or ultraviolet rays. The resulting excitation state is temporary, meaning that it is lost in a very short period (10-9 of a second to several seconds). In many cases, the excitation energy is lost in the form of heat, but The excitation energy of some substances is lost in the form of the emission of radiant energy, and this is generally known as luminescence. Fluorescence is considered a type of luminescence in which emission occurs at a high speed in a time of (10-6-10-9 seconds). Phosphorescence is considered a type of luminescence in which emission occurs slowly in a time of (103 -10) seconds.
Difference Between Fluorescence and Phosphorescence
Fluorescence and phosphorescence are two mechanisms of light emission or are examples of photoluminescence (photoluminescence, photoluminescence or photoluminescence: the same terms with the same meaning). However, the terms fluorescence and phosphorylation do not mean the same thing nor do they occur in the same way. In both fluorescence and phosphorylation, the molecules absorb light and emit (radiate) photons of lower energy (the longest wavelength), but the fluorescence process occurs much faster than phosphorylation and does not change the direction of electron spin. Below is an explanation of how photoluminescence works and a look at the processes of fluorescence and phosphorylation, with familiar examples of each type of light emission. Photoluminescence Basics Photoluminescence occurs when molecules absorb energy. If the light causes an electron to be excited, then in this case the particles are called excited particles. If the light causes vibrational excitation, the molecules become hot. Particles can become excited by absorbing different types of energy, such as physical energy (light), chemical energy, or mechanical energy (for example, friction or pressure). The absorption of light or photons may cause the molecules to become hot and excited. When the molecules become excited, the electrons are moved to a higher energy level. When they return to a lower, more stable energy level, photons are emitted, which appear as photoluminescence. There are two types of photoluminescence, fluorescence and phosphorylation. How does the fluorescence process happen: In the case of fluorescence, high-energy light (short wavelength, high frequency) is absorbed. which puts the electron into an excited energy state. Usually, the absorbed light is in the ultraviolet range, the absorption process occurs quickly (within a period of time of 10-15 seconds) and there is no change in the direction of electron spin. The fluorescence process happens so fast that if you turn off the light, the material stops glowing. Also, the color (wavelength) of the light emitted by the fluorescence process is almost different from the wavelength of the incident light. There is no change in the direction of electron spin. The fluorescence process happens so fast that if you turn off the light, the material stops glowing. Also, the color (wavelength) of the light emitted by the fluorescence process is almost different from the wavelength of the incident light. In addition to the visible (radiated) light emitted, infrared light is also radiated. Vibrational relaxation usually results in the emission of infrared light about 10-12 seconds after the radiation has been absorbed. When the electron returns to its stable level, it emits visible and infrared light and occurs about 10-9 seconds after the energy is absorbed. The difference in wavelength between the absorption and emission spectra of a fluorescent substance is called the Stokes shift. Examples of fluorescence: Fluorescent lamps and neon panels are examples of fluorescence, as do materials that glow under a black light, but stop glowing once UV rays are turned off. Also, some scorpions can fluoresce if black light is shined on them, they glow as long as ultraviolet light is available, however, the animal's exoskeleton does not protect them well from radiation, so you should not keep the black light on for long to see the scorpion glow. Some corals and fungi also fluoresce. And many highlighters (fluorescent pens) are also fluorescent. How does phosphorylation work: Like in fluorescence, the phosphorescent material absorbs high-energy light (usually ultraviolet), causing the electrons to move to a higher energy state, but the transition to a lower energy state occurs more slowly and the direction of electron spin may change. Phosphorescent materials may appear to glow for several seconds to two days after the light is turned off. The reason that phosphorylation lasts longer than fluorescence is because the excited electrons jump to a higher energy level than in the case of fluorescence. So the electrons have more energy to lose and may spend time at different energy levels between the excited and the steady state. And as we mentioned earlier, the electron does not change its spin direction in the case of fluorescence, but it can do so if the conditions are suitable during phosphorylation. This rotation may occur during or after energy absorption. If the rotation reversal does not occur, the molecule is said to be in a single state. And if the electron undergoes a reversal of the spin, a triple state of the molecule is formed. Tertiary states usually have a long lifetime, as the electron will not return to its lower energy state until it returns to its original state (the original spin state). Because of this delay, the phosphorous materials appear to "glow in the dark". Examples of phosphorescence: phosphorous materials in gun shots used for toys, glow-in-the-dark phosphorous stars, paint used to make star paintings