Excitation and Emission Wavelengths of UV Fluorescent Pigments: A Technical Guide to 365 nm and 254 nm Series Selection
Published by Nichwell Technical Team
Nichwell is a professional manufacturer of UV fluorescent pigments and thermochromic pigments, supplying specialty colorant solutions to security printing, coatings and plastics customers across more than 30 countries.
1. What Are Excitation and Emission Wavelengths?
UV fluorescent pigments work by absorbing ultraviolet light at a specific wavelength — the excitation wavelength — and re-emitting that energy as visible light at a longer wavelength — the emission wavelength. This process is known as photoluminescence.
Two parameters define the optical behavior of every UV fluorescent pigment:
Excitation Wavelength
The wavelength at which the pigment absorbs ultraviolet energy most efficiently. The pigment must be exposed to UV light at or near its excitation wavelength to produce strong, reliable fluorescence. Industrial UV fluorescent pigments are typically designed for excitation at:
365 nm — Long-wave ultraviolet (UV-A)
254 nm — Short-wave ultraviolet (UV-C)
Emission Wavelength
The wavelength of visible light emitted by the pigment after excitation. The emission wavelength determines the fluorescent color observed by the human eye.
Typical emission peaks and corresponding colors:
440 ± 5 nm → Blue fluorescence
494 ± 5 nm → Green fluorescence
530 ± 5 nm → Yellow-green fluorescence
544 ± 5 nm → Yellow fluorescence
580 ± 5 nm → Orange fluorescence
610 ± 5 nm → Red fluorescence
The combination of excitation wavelength and emission wavelength determines whether a pigment is suitable for a specific application, verification system and security requirement.
For further reference on photoluminescence principles, see:
IUPAC Recommendations on Luminescence Terminology
2. Why Does Excitation Wavelength Selection Matter?
Selecting an incorrect excitation wavelength for your application can lead to the following problems:
No Fluorescence Response
If your verification equipment operates at 254 nm and you select a pigment optimized for 365 nm excitation, the pigment will produce little or no detectable fluorescence under your verification system. The security feature will fail entirely.
Significant Loss of Brightness and Color Purity
Even when a pigment shows some response at a non-optimal excitation wavelength, fluorescence brightness and spectral purity are substantially reduced. This directly affects print quality and verification reliability.
Incompatibility with Verification Equipment
In security printing, printed features are verified using fixed-wavelength UV equipment. The excitation wavelength of the pigment must match the emission wavelength of the verification light source to ensure consistent, reliable authentication results.
Matching excitation wavelength to your verification system is a fundamental requirement before formulation development begins.
3. 365 nm UV Fluorescent Pigment Series
Organic Series
Nichwell’s 365 nm organic UV fluorescent pigments are engineered for security ink and printing applications requiring bright fluorescence and low daylight visibility.
Key properties:
- High fluorescence brightness with vivid color emission
- Particle size range: 1–15 µm, with grade options available
- Daylight appearance: off-white to lightly tinted powder, providing low daylight visibility in printed films
- Suitable for compatible offset, flexographic, gravure and screen-printing systems. Dispersion behavior and solvent compatibility should be evaluated in the customer’s actual binder and ink formulation before production use.
Available Colors and Emission Data — 365 nm Organic Series:
| Color | Daylight Appearance | Fluorescence Under 365 nm | Emission Peak | Particle Size |
|---|---|---|---|---|
| Red | Pinkish powder | Bright Red | 610 ± 5 nm | 1–15 µm |
| Green | Off-white powder | Green | 494 ± 5 nm | 1–10 µm |
| Yellow-Green | Off-white powder | Bright Yellow-Green | 530 ± 5 nm | 1–10 µm |
| Blue | Off-white powder | Blue | 440 ± 5 nm | 1–10 µm |
| Yellow | Off-white powder | Bright Yellow | 544 ± 5 nm | 1–10 µm |
| Orange | Off-white powder | Orange | 580 ± 5 nm | 1–10 µm |
| White | Light-yellow powder | White (Dual Peak) | Peak I: 449 ± 5 nm / Peak II: 539 ± 5 nm | 3–8 µm |
Technical Note: All data presented in this table are typical reference values and do not constitute a product specification. Actual performance varies by grade, formulation, substrate and processing conditions. Application testing is required before commercial use.
Inorganic Series
Nichwell’s 365 nm inorganic UV fluorescent pigments are designed for applications requiring improved thermal stability and weathering performance compared to organic grades.
- Typical applications include:
- Exterior coatings and powder coatings Ceramics and glass marking
Plastic masterbatch
Available colors: Inorganic Red, Yellow, Green, Yellow-Green, Blue, Orange, White, Purple.
Particle size range: 1–10 µm.
Selected inorganic grades offer improved thermal stability and weathering resistance compared to organic series pigments, making them suitable for higher-temperature processing environments and demanding outdoor applications.
Important: Thermal stability limits vary significantly by color, chemical composition, grade, exposure time and processing conditions. Performance data for specific grades under defined conditions do not represent the general performance of the entire inorganic series. Please share your processing temperature profile with our technical team before selecting a grade for high-temperature applications.
Typical Applications — 365 nm Series
- Security inks: compatible offset, flexographic, gravure and screen-printing systems
Covert printing: labels, certificates, tax stamps and document verification
Brand authentication: packaging and invisible product markings
Security coatings: UV-responsive identification and inspection markings
Plastics: compatible masterbatch for authentication applications
Industrial inspection: process control and invisible marking
Final suitability depends on the formulation, substrate, processing conditions and regulatory requirements of the finished product. Application testing is required.
4. 254 nm UV Fluorescent Pigment Series
Application Scope
254 nm excitation (UV-C short-wave ultraviolet) is used in high-security authentication applications where covert features must remain invisible under standard long-wave UV verification equipment.
Typical applications include:
- Banknote, identity document and tax stamp security printing
- Forensic evidence marking and chain-of-custody tracking
- High-security printing and authentication applications
254 nm fluorescent features cannot be excited by standard 365 nm UV lamps, providing an additional level of covert security that requires specialized short-wave UV verification equipment to detect.
Safety Notice
254 nm UV sources (UV-C) require suitable shielding, eye protection and safe operating procedures. Operators must follow applicable safety regulations and standards when working with 254 nm UV equipment. Please consult your equipment supplier and relevant workplace safety guidelines before use.
For reference on UV-C radiation safety:
ICNIRP Guidelines on Ultraviolet Radiation
WHO UV Radiation Safety Information
Organic and Inorganic Options
The 254 nm series is available in both organic and inorganic formulations to meet different requirements for thermal stability, weathering resistance and spectral purity.
Available Colors and Emission Data — 254 nm Series:
| Product Type | Daylight Appearance | Fluorescence Under 254 nm | Emission Wavelength / Range | Particle Size |
|---|---|---|---|---|
| Organic Red | Off-white powder | Red | 610 ± 5 nm | 2–6 µm |
| Organic Orange | Off-white powder | Orange | 580 ± 5 nm | 2–6 µm |
| Organic Yellow | Off-white powder | Yellow | 560 ± 5 nm | 2–6 µm |
| Organic Green | Off-white powder | Green | 520 ± 5 nm | 2–6 µm |
| Inorganic Red | Off-white powder | Red | 600–700 nm | 1–10 µm |
| Inorganic Yellow | Off-white powder | Yellow | 550–600 nm | 1–10 µm |
| Inorganic Blue | Off-white powder | Blue | 400–500 nm | 1–10 µm |
| Inorganic Green | Off-white powder | Green | 500–570 nm | 1–10 µm |
Technical Note: All data presented in this table are typical reference values and do not constitute a product specification. Actual performance varies by grade, formulation, substrate and processing conditions. Application testing is required before commercial use.
5. 365 nm vs 254 nm: Core Comparison
| Parameter | 365 nm Series | 254 nm Series |
|---|---|---|
| Excitation Wavelength | 365 nm (UV-A, long-wave) | 254 nm (UV-C, short-wave) |
| Verification Equipment | Standard UV lamps, widely available | Specialized short-wave UV equipment required |
| Covert Security Level | Standard | High — invisible under 365 nm UV |
| Daylight Visibility | Low — off-white or lightly tinted powder | Very low |
| Chemistry | Organic / Inorganic | Organic / Inorganic |
| Typical Applications | Security inks, labels, certificates, tax stamps, packaging | Banknotes, ID documents, tax stamps, forensic marking |
| Operational Safety | Standard UV-A precautions | UV-C shielding and eye protection required |
6. How to Select the Right Series for Your Application
Before selecting between the 365 nm and 254 nm series, clarify the following parameters:
1. What UV wavelength does your verification equipment use?
This is the primary selection criterion. The pigment excitation wavelength must match the emission wavelength of your verification light source. If your verification process uses standard long-wave UV lamps, select the 365 nm series. If your process uses specialized short-wave UV verification equipment, select the 254 nm series.
2. What level of covert security is required?
If your application requires features that are completely invisible under standard 365 nm UV verification lamps, the 254 nm series provides a higher level of covert security. For standard security ink applications, the 365 nm organic series is the most widely used solution.
3. What are your processing conditions and temperature requirements?
Thermal stability varies significantly between grades. For high-temperature processing environments such as plastics extrusion or powder coatings, inorganic grades are generally preferred. However, the thermal stability limit of each specific grade depends on color, chemical composition, grade, exposure time and processing conditions. Please provide your processing temperature profile and consult our technical team before selecting a grade.
4. What is your binder and ink system?
Pigment compatibility with binders, solvents and other formulation components must be evaluated in the customer’s actual system. To receive a grade recommendation for testing, please provide:
- UV excitation wavelength
- Binder or resin system
- Processing temperature
Target emission color
7. Custom Colors and Emission Characteristics
For high-security applications where standard color series do not meet specific spectral requirements, custom colors, blends and emission characteristics may be available, subject to technical feasibility and minimum order requirements.
- To initiate a custom evaluation, please provide:
- Target excitation wavelength
- Target emission color or emission peak range
- Ink or coating system description Substrate type
Processing temperature range
8. Quality Control and Batch Consistency
In security printing applications, batch-to-batch spectral consistency directly affects the reliability of automated and manual verification systems.
Nichwell evaluates each production batch of UV fluorescent pigments against defined specifications for:
- Emission wavelength
- Fluorescence brightness
Particle size distribution
Batch-specific test data are available for selected grades upon request. Products are manufactured under an ISO 9001-certified quality management system. Selected third-party test reports are available upon request.
For reference on quality management standards:
ISO 9001:2015 Quality Management Systems
9. Technical Data Disclaimer
All excitation wavelength, emission peak and particle size data presented in this article are typical reference values for general guidance only. They do not constitute a product specification, performance guarantee or warranty of any kind.
Actual pigment performance is influenced by grade selection, formulation composition, substrate type, processing conditions and environmental factors.
Customers should conduct thorough application testing under their intended formulation and processing conditions before commercial use. Nichwell’s technical team is available to support grade selection, sample evaluation and application development.
To request TDS, SDS or test samples for specific grades, please contact the Nichwell technical team.
Summary: Key Selection Criteria
Step 1 — Confirm your verification equipment UV wavelength: 365 nm or 254 nm
Step 2 — Determine required covert security level
Step 3 — Define processing temperature and thermal requirements
Step 4 — Identify binder, solvent and ink system
Step 5 — Request grade recommendation, TDS and test sample
Step 6 — Conduct application testing in your actual formulation
Step 7 — Confirm batch consistency requirements before production
Request a Sample or Technical Consultation
Tell us your UV wavelength, binder system, processing temperature and target emission color. Our technical team will recommend a suitable grade for evaluation.