Optical characteristics of luminescent pigments for inks 1

This type of pigment is completely different from the general pigment, and it has a completely new concept in optical properties.

The difference between luminescent pigments and general pigments lies in the fact that the former can absorb certain forms of energy and convert it into photon with emission energy in the heat emission, thus causing luminescence. For general pigments, they can only convert the absorbed energy into heat in the visible region or near visible region, so there is no luminescence phenomenon.

The color of a typical pigment has only selective reflection in the visible spectrum. This selective absorption and reflection gives the general pigment a color. Some absorb the spectrum of this kind of spectral reflectance, and some absorb that kind of spectral reflectance of this kind of spectrum, thus forming countless colors. The colors of the luminescent pigments can all emit rays or be combined with other emitted rays. It does not have much absorption effect in the visible spectral region.

When the blue and yellow colors of the general pigment are equally mixed, green color is obtained (red and blue are subtracted). When the blue and yellow luminescent pigments are properly mixed, white or highly saturated color light is obtained.

Some materials emit visible light after being irradiated with ultraviolet light and have a brilliant sense of color. This phenomenon of absorbing invisible light and emitting visible long-wavelength light is called a cold glow phenomenon. When (ultraviolet) light ceases to illuminate, the substance that stops emitting light is called a fluorescent (body) substance, and if it continues to emit light, it is called a phosphorescent (body) substance.

Luminescent Pigments are sometimes transliterated into Luminescent Pigments. Generally divided into organic and inorganic two categories, the former mainly refers to daylight fluorescent pigments, and the latter refers to zinc sulfide, cadmium sulfide pigments.

Daylight fluorescent pigments are now widely used in the ink and coating industry.

First, organic light-emitting pigments

Organic light-emitting pigments currently mainly refer to daylight fluorescent pigments.

Fluorescent pigments have the property of absorbing light at specific frequencies and regenerating these absorption energies at low rates (long wavelengths). Many natural products such as quinine and various mineral phosphors are only sensitive to ultraviolet light, and many synthetic organic compounds and inorganic pigments can only generate bright fluorescence in the visible spectrum under the excitation of strong ultraviolet light. color.

What is to be discussed here is a pigment that can generate fluorescence after being excited in the ultraviolet region and the visible spectrum region. In the case of daylight fluorescent pigments, because its emission light also includes (additional) ordinary reflection colors, thereby enhancing its emission range (energy), it looks stronger than daylight.

(I) Composition characteristics

Luminescent pigments can increase brightness and visibility due to fluorescence. After they absorb energy, almost all molecules are excited in the low energy state (ground state). Due to the absorption of the quantum emitted in the ultraviolet region and the visible region, the time is very short (about 10-5 seconds), and as a result, electrons are transited to orbits of higher energy levels. When this transition occurs, it can be said that the molecule is in an excited state. A molecule can have many excited states, and each excited state has a certain form of vibration. Absorption of emission energy by a molecule is a quantum process. The energy of photons (photons) can be defined as E=hv, E is energy, h is Planck's constant, and v is the frequency of light absorption. The absorbed energy corresponds to the change in the state of one molecule, and it must be strictly equal to the energy of the photon. For a given molecule, it can only absorb quantum of a certain frequency, and the molecular structure of matter determines these frequencies. For many molecules, their absorption bands are wide, including daylight fluorescent pigments.