The original luminous material for watches was radium (Ra). In 1898, Marie Curie discovered the element radium, which emits light blue light as it continues to decay. After the radium element is mixed with zinc sulfide, it can emit light by itself without being exposed to a light source.
In 1915, it was used in products by Panerai, an Italian military watch at that time, and applied for a patent. Therefore, since the 1930s, a mixture of radium and zinc sulfide has been widely used in the luminous coating of watches.
When light irradiates certain atoms, the energy of the light causes some electrons around the nucleus to jump from their original orbits to higher energy orbits, that is, from the ground state to the first excited singlet state or the second excited state. Singlet, etc.
The first excited singlet state or the second excited singlet state is unstable, so it will return to the ground state. When the electron returns to the ground state from the first excited singlet state, energy will be released in the form of light. So fluorescence is produced.
Fluorescence is the light emitted by a substance after absorbing light or other electromagnetic radiation. In most cases, the emission wavelength is longer and has lower energy than the absorption wavelength. However, when the absorption intensity is large, two-photon absorption may occur, causing the radiation wavelength to be shorter than the absorption wavelength. When the radiation wavelength is equal to the absorption wavelength, it is vibrational fluorescence.
A common example is that a substance absorbs ultraviolet light and emits fluorescence in the visible band. This is the principle of the fluorescent lamps in our lives. The phosphor coated on the lamp tube absorbs the ultraviolet light emitted by the mercury vapor in the lamp tube, and then The phosphor emits visible light, making it visible to the human eye.
Extended information:
Physical parameters:
1. Excitation spectrum: When the luminescent material is excited by light of different wavelengths, the cadmium selenide quantum dots of the material The relationship between the intensity of a certain emission spectrum line and the band or the luminous efficiency and the wavelength of the excitation light that fluoresces under the irradiation of ultraviolet rays.
2. Emission spectrum: the change in the luminous intensity of different wavelengths of a luminescent material when excited by a certain excitation light.
3. Fluorescence intensity: Fluorescence intensity is related to factors such as the fluorescence quantum yield, extinction coefficient and content of the substance.
4. Fluorescence quantum yield Q: Quantum yield represents the ability of a substance to convert absorbed light energy into fluorescence. It is the ratio of the number of photons emitted by a fluorescent substance to the number of photons absorbed.
5. Stokes shift: Stokes shift is the difference between the maximum fluorescence emission wavelength and the maximum absorption wavelength.
6. Fluorescence lifetime: When a beam of light excites a fluorescent substance, the molecules of the fluorescent substance absorb energy and transition from the ground state to an excited state, and then emit fluorescence in the form of radiation back to the ground state, and the excitation stops. When, the time required for the fluorescence intensity of a molecule to decrease to 1/e of the maximum intensity during excitation is the fluorescence lifetime.
Baidu Encyclopedia—Fluorescence