Color measurement of fluorescent materials by spectrophotometer

Fluorescent materials are made of metal (zinc, chromium) sulfide or rare earth oxide and trace active agent by calcination. The color is generally colorless or light white. It is the visible light (400-800nm) of various colors under the irradiation of ultraviolet light (200-400nm), depending on the type and content of metal and activator in the pigment. Fluorescent materials absorb light of a certain wavelength and immediately emit light of different wavelengths outward, which is called fluorescence.

When the incident light disappears, the fluorescent materials will immediately stop emitting light. More specifically, fluorescence refers to some quite bright color lights, such as green, orange and yellow, which are seen by the human eye under the external light. People often call them neon lights. LISUN lauched the HSDC-920 spectrophotometer adopts four ultraviolet measurement modes, making fluorescence invisible.

With the progress of science and technology, more and more people have studied fluorescence, and the application range of fluorescent substances is becoming wider and wider. In addition to being used as dyes, fluorescent substances are also widely used in the fields of organic pigments, optical brighteners, photooxidizers, coatings, chemical and biochemical analysis, solar collectors, anti-counterfeit labels, drug tracing and lasers. Therefore, it is of great significance to study and discuss the color measurement of fluorescent materials by spectrophotometer.

According to Stokes’ law, when the fluorescence material absorbs the incident radiation energy, the excited fluorescence molecule will emit longer radiation than the absorbed incident wavelength when returning to the ground state.

When the fluorescent material illuminated by the light source is visually observed, the human eye will see all spectral radiation within the visible range, that is, the reflection (or transmission) spectrum of the material to the light source and the fluorescence emission spectrum of the material will be observed at the same time. Therefore, when the color of fluorescent materials is measured by physical methods, the measurement results must be consistent with the visual evaluation, otherwise wrong conclusions will be obtained.

The commonly used color measurement methods of fluorescent materials include monochromatic light excitation measurement and composite light irradiation measurement.
1. Monochromatic light excitation measurement
The principle is to irradiate the sample with monochromatic light of a specific wavelength µ by excitation monochromator, and then measure the wavelengths of the visible band with the analytical monochromator λ Radiance factor of β ( λ, µ)。 The corresponding radiance factor is measured for different incident wavelengths β ( λ, µ), when the incident radiation spectrum distribution is S (µ) λ Relative spectral distribution of reflection and emission of R（ λ)

2. Combined light irradiation method
The characteristic of compound light irradiation measurement method is that the excitation light source is directly illuminated by the compound light source. Directly measure the spectral radiance factor of the fluorescent material under the illumination of the light source used in the test β ( λ)， Thus, the tristimulus value is calculated. The results are only limited to the objective effect of a specific light source, and it is impossible to calculate the color characteristics of this fluorescent material under another light source.

Spectrometric method:
In practical applications, it is not easy to accurately simulate the spectral distribution of the standard illuminator, especially to simulate the standard. Therefore, the above measurement method using a monochromator has low accuracy, and the obtained surface reflects the performance of fluorescent materials. In order to overcome the above defects, a dual-path spectrophotometer measurement system can be used. A spectrograph is added to the optical path. The full-spectrum light source is divided by different wavelengths through the grating to obtain the spectral radiance factor of the reflected light of the sample at each wavelength. After comparing with the spectral radiance factor of the light source, the chromaticity parameters of the fluorescent sample can be calculated.

LISUN lauched Benchtop Spectrophotometer (Reflectance and Transmittance) DSCD-920 adopts 7 inches touch screen, full wavelength range, Android operate system. Illumination : reflectance D/8° and transmittance D/0°(UV included / UV excluded), high accuracy for color measurement, large storage memory, PC software, because of above advantages, it is used in laboratory for color analysis and communication.

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