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Ultimate Guide to Fluorescent Pigments and Dyes

Stacks of money fill the frame

What Are Fluorescent Pigments and Dyes?

Pigments and dyes are chemical substances used to color another material (often referred to as colorants).  Fluorescent pigments and dyes are special colorants that absorb light energy at one wavelength, such as invisible ultraviolet light (UV), and then emit light at a longer wavelength, producing a specific color.

Another way of describing the fluorescence process is that higher energy light (shorter wavelength = higher energy) excites fluorescent material to emit lower energy visible light (longer wavelength = lower energy). Fluorescent materials can emit different colors throughout the visible color spectrum depending upon their physical and chemical properties.

For are more information regarding fluorescence and how it relates to phosphorescence and photoluminescence in general, see our blog Basic Chemistry 101: Understanding Photoluminescence, Fluorescence, and Phosphorescence.

The Two Main Types of Fluorescent Colorants

Visible Fluorescent Pigments and Dyes

Visible fluorescent pigments and dyes are visible colorants that become brighter when excited by light. These colors are usually referred to as daylight-fluorescent colors and enhance the visible color reflected by the material to produce an intense glow.

The primary characteristic of daylight-fluorescent materials is their extremely high visibility and ability to attract attention. This attribute makes them ideal for:

Yellow fluorescent powder under UV light
  • Advertising 
  • Road safety 
  • Protective clothing
  • Theater/performing arts 
  • Consumer products (toys, paints, highlighter pens, tags, and labels)

Invisible Fluorescent Pigments and Dyes

Invisible fluorescent pigment and dyes are colorants that possess little or no visible color under standard white light. The material will only emit a visible color while excited by light of a shorter wavelength, such as invisible ultraviolet light (UV). The color is only visible for as long as the excitation is maintained.  Once removed from the excitation light, the material stops producing the visible color.

In addition, some materials will emit different colors depending on the specific wavelength of UV light. This characteristic makes invisible fluorescent pigments and dyes ideal for applications requiring hidden or covert features such as:

  • Document security
  • Brand protection 
  • Identification verification 
  • Counterfeit prevention
  • Process control,
  • Defect detection

In addition, invisible fluorescent materials have many medical and scientific research applications. 

What Are the Differences between Fluorescent Pigments and Dyes?

Fluorescent pigments and dyes are usually powdered compounds integrated with other media so that they can be printed or embedded directly in another material, such as plastics and adhesives. The powder is dispersed (pigments) or dissolved (dyes) in inks, polymers, water, oils, adhesives, solvents, and/or other media.

Fluorescent pigments and dyes have a number of similarities. For instance, both are used as colorants and can be natural or synthetic. They also fluoresce under similar conditions and emit various colors throughout the spectrum. However, pigments and dyes, whether fluorescent or non-fluorescent, have several different properties. These materials provide different advantages depending upon the application. The fundamental differences between pigments and dyes include:

Multicolored inks using fluorescent detectors

Dyes are typically soluble in water, and pigments are insoluble both in it and many other solvents (with a few exceptions). Pigments are usually dispersed or suspended in a medium or a chemical binder.

Dyes have very small particle sizes while pigments have comparatively large particle sizes. The relative size difference between dyes and pigments can be imagined as the size difference between a grain of sand and a football.

Dyes tend to be more transparent or translucent than pigments due to their solubility and smaller particle size. Pigments are typically less transparent due to their larger particle size and the properties of the binder used to integrate the pigment into media or the substrate.

Lightfastness is a visible colorant’s resistance to fading when exposed to light over time. In the case of invisible fluorescent material, this quality is the resistance to the material losing fluorescent intensity when exposed to light over time. Overall, pigments have much greater lightfastness than dyes, but both vary depending on the specific compound. 

Often, a dye can attach itself chemically to a substrate, becoming part of the material on a molecular level. Alternatively, a pigment typically requires a carrier to bind the pigment onto the substrate.

Dyes are generally comprised of carbon-based organic materials. However, pigments can be made of either organic or inorganic mineral-based substances.

The History of Fluorescent Pigments and Dyes

Fluorescent pigment and dye development began in the late 19th century. In 1871, Adolf von Baeyer produced the first synthetic fluorophore pigment from phthalic anhydride and resorcinol.  From the 20th century through the present day, materials and methods have evolved to include a vast array of both organic and inorganic compounds. Below is a brief timeline of important people & events in the history of fluorescent pigments and dyes:

Johann Wilhelm Ritter discovered Ultraviolet light
George Gabriel Stokes wrote a famous paper on the change of wavelength of light. In this paper, he described the phenomenon of fluorescence and he also discovered naturally occurring fluorescence in minerals. Stokes Law and Stokes Shift are named after him. Stokes' Law states that the fluorescence emission occurs at a longer wavelength than the incident light. The Stokes Shift is an important concept in Fluorescence Spectroscopy.
George Gabriel Stokes wrote a famous paper on the change of wavelength of light. In this paper, he described the phenomenon of fluorescence and he also discovered naturally occurring fluorescence in minerals. Stokes Law and Stokes Shift are named after him. Stokes' Law states that the fluorescence emission occurs at a longer wavelength than the incident light. The Stokes Shift is an important concept in Fluorescence Spectroscopy.
William Henry Perkin discovered the first synthetic dye as a commercial colorant. Mauve was developed from aniline, a coal tar derivative.
Adolf von Baeyer was a German chemist who produced the first synthetic fluorophore. Baeyer named this compound resorcinphthalein. Today this chemical is known as fluorescein.
Maurice Ceresole, an industrial chemist, successfully synthesized a new class of highly fluorescent dyes with red-shifted spectra. He named them Rhodamines.
Albert Coons and colleagues were the first to devise a method to visualize proteins in animal tissue by conjugating antibodies to fluorescein, a method we know today as immunofluorescence
Joseph and Robert Switzer are credited for inventing black light paint in the 30’s and later developed daylight fluorescent paints. They founded Switzer Brothers, Inc. (now known as Day-Glo Color Corp.)
Alan Waggoner was a chemist who synthesized and patented cyanine based dyes that are photostable, water-soluble, and non-cytotoxic for biomedical research.

What Are Fluorescent Materials Made of?

Pictured: There's a grayish/blue background. Hanging in front are a row of block strings with long thing fluorescent lights attached to them

Before the late 18th century, all pigments and dyes were made from naturally occurring organic (plants, ash) or inorganic materials (minerals such as azurite and cinnabar).

Synthetic processes were later developed to copy vegetable, animal, and mineral-based colorants in controlled conditions to increase the quality, purity, and consistency of the colorants.

Fluorescent pigments and dyes contain or are made entirely of chemical compounds known as fluorophores. Fluorophores are molecules that absorb light energy at particular wavelengths and energy level (absorption), reach an excited state (excitation) and then emit light at longer wavelengths at a lower energy level (emission)—usually in the form of a visible color.

The composition of fluorescent pigments and dyes varies according to the fluorophore’s ability to absorb a range of wavelengths of light energy and also emit a range of wavelengths. Most colors in the visible spectrum can be produced by different fluorophores.

How Are Fluorescent Pigments and Dyes Made?

Chemists design, synthesize and manipulate complex compounds to make materials that fluoresce in all colors. These formulations are specifically designed to meet strict application specifications. The composition, formulation, and design of fluorescent pigments and dyes for security applications are usually proprietary.

In some cases, particularly for daylight fluorescent pigments, the pigment is made from a fluorescent dye that has been combined with resins and polymers. In the case of specialized invisible fluorescent pigments, the molecule itself is fluorescent and has no or little visible color. This quality allows it to remain undetected unless exposed to UV light, as seen in anti-counterfeiting measures in currency.

Powder that has been excited by fluorescent light

Why do Fluorescent Materials React to UV Light?

Fluorescent pigments and dyes work using the same principle. The fluorophores in the pigment or dye absorb light energy at particular wavelengths and energy level (absorption), reach an excited state (excitation) and then emit light at longer wavelengths at a lower energy level (emission)—usually in the form of a visible color.

Related post: Understanding Absorption, Emission, and Excitation in Fluorescence

Importantly, this process registers visually as an emitted color independent from the visible or reflected color of the pigment or dye and can be wholly different. Also, the visual results vary greatly depending upon whether the fluorescent colorants are visible or invisible:

Visible Pigments and Dye Colorants

In the case of visible fluorescent pigments and dyes, the normally reflected color of the pigment or dye is visible under standard white light and then enhanced or amplified by the emitted fluorescent color when it is excited by UV light; we refer to these materials as daylight-fluorescent.

Invisible Pigments and Dye Colorants

In the case of invisible fluorescent pigments and dyes, the material has little or no visible color under standard white light. The material will only emit a visible color while it is excited by UV light. The color is only visible for as long as the UV excitation is maintained. Importantly, these invisible pigments and dyes can be used in small concentrations in other media, such as printing ink and plastics.  This allows the additives to remain completely invisible unless exposed to UV light of a certain wavelength.

The specific UV excitation wavelength required and the color emitted by fluorescent colorants vary depending on the properties of the fluorophore. The engineer must use the correct media and formulation for the material to fluoresce as desired.

Angstrom Technologies, Inc., specializes in designing and producing fluorescent materials to work as desired in specific media, with specified substrates, and to integrate these materials successfully in finished applications. 

What is a UV Pigment/UV Dye?

UV Pigments and UV Dyes are just alternate terms for UV Fluorescent Pigments and UV Fluorescent Dyes. It means the pigment or dye contains fluorophores that can be activated by UV light excitation and will fluoresce.

What is UV Fluorescent Ink?

UV fluorescent ink is an ink or similar liquid with an added UV fluorescent pigment or dye.  The additive must be chemically and physically compatible with the ink and the printing process for which it is intended.  As previously stated, the fluorescent colorant must be engineered properly for the final product to fluoresce as desired.

Phosphorescent Colorants

Similar to fluorescent materials, phosphorescent colorants work the same as they are both photoluminescent materials.  The technical differences between fluorescence and phosphorescence are complex, but the basic difference between the two is how long the material will emit light after the UV light is removed.

Fluorescent material stops emitting light in a very short time after the excitation. In many cases, the color emitted by fluorescent materials will seem to disappear instantaneously when the excitation stops.

In contrast, phosphorescent material can emit a visible color for a long time after the excitation, creating a lasting glowing effect or afterglow. The phosphorescent afterglow may persist for a few seconds, minutes, or hours depending on the properties of the material. The duration also depends on the intensity of the excitation and the amount of time it was exposed to the excitation light source.

Non-Fluorescent Materials with Optical Effects

There are a variety of other materials that produce effects similar to fluorescent and phosphorescent pigments and dyes. Individuals sometimes confuse these media that produce optical effects with fluorescence. However, their similarities have nothing to do with fluorescence or luminescence in general. These materials include:

Ink made from OVP displays two distinct colors. The color shifts as the viewer changes their angle or the angle of the light source. OVP pigments are multi-layer films of semi-transparent reflector (metals) and dielectric materials.

Photochromic colorants change color when exposed to a change in ambient lighting, and the color persists for a certain length of time before returning to the original or absence of color. A well-known example of

Thermochromic colorants to change color depending on temperature exposure. The process is temporary as the color reverts when the heat source is removed.

What Industries Use Fluorescent Pigments and Dyes?

Fluorescent materials are used by government agencies, secure document producers/processors, and other businesses for authentication, brand protection, and anti-counterfeiting applications. Fluorescent materials produced for these industries are designed to work with a variety of components such as adhesives, plastics, bindings, threads, and other materials. These materials are then integrated or applied to the end product in highly discreet and controlled processes.

UV Fluorescent materials are also used by numerous industries for manufacturing process control, parts, and surface defect detection and in the biomedical/biomedical research industries for research. 

Daylight fluorescent and phosphorescent materials are used in numerous industries, including include advertising, safety equipment, and arts and entertainment.

Currency Anti-Counterfeit features, tax stamps, passports

Identification documents, licenses, corporate ID’s

Brand authentication, track and trace, event tickets

Document security, financial certificates and securities authentication

Automated Process Control, surface defects detection, leak detection

Fluorescent materials used extensively in research and engineering

Daylight fluorescent & phosphorescent signage, equipment marking, emergency exit controls

Fuselage defect detection (fluorescence), safety marking and equipment (daylight fluorescent and phosphorescent)

Daylight fluorescent packaging, print media

Phosphorescent & daylight fluorescent used for special effects, art materials and safety

How Do Fluorescent Pigments and Dyes Prevent Counterfeit Currency?

Sheets of counterfeit money sit on top of a printer.

Fluorescent components in currency are frequently used to make the process of counterfeiting more difficult, especially when used in conjunction with other security features.

For instance, in US currency it is the lack of fluorescence in the paper that is an important indicator of legitimacy. The paper’s special mix of cotton and linen makes it appear dull under UV light compared to most other paper, which looks bright blue due to the presence of optical brighteners.

American currency additionally uses a small plastic strip or thread embedded in the bill that fluoresces a specific color when exposed to UV light, depending on the denomination of the bill. The placement of this strip is further dependent on the bill’s denomination. For example, the embedded strip in $100 bills glow a pinkish red when exposed to UV light and are imprinted with USA and the number 100 in an alternating pattern on both sides of the strip.

Many other currencies worldwide embed invisible fluorescent fibers, patterns and/or graphic images that are only visible when exposed to UV light.

You can easily evaluate currencies through a detection device, like the MoneyChecker LED 425.  We design this tool specifically to authenticate the UV security features in US currency.

How Do Fluorescent Materials Help Prevent Counterfeit IDs and Branded Products?

Security Documents & ID

Invisible ID security features can be as simple as a hidden mark printed conventionally or as complex as a full-color invisible photo that matches the photo ID. In other security documents, invisible UV fluorescent materials are used alone or in conjunction with other methods to protect the authenticity of various financial certificates and securities, such as stock certificates, travelers’ checks, and more.

Retail & Brand Protection

Invisible UV fluorescent marks and codes incorporated into a retailer’s existing label, tag, or another item can provide a very cost-effective method for brand authentication without altering the original visible label design. This method is very flexible and allows for various levels of complexity; it can be a simple invisible mark, added to enhance a visible ink, combined with other security marks, or used to produce an invisible track code.

Angstrom Technologies, Inc. Is the Expert

Angstrom Technologies, Inc. specializes in the development, custom formulation, and manufacture of invisible fluorescent pigments and dyes to exact specifications for specialized applications that require integration with a wide variety of materials, such as inks, varnishes, plastics, and adhesives. Our products are designed for numerous industries and are excellent choices for document security, process control, and other applications. If you’re interested in learning how we can help, reach out to us today. 

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