Exploration of Red and NIR Long Afterglow Materials

Long afterglow self-luminous material is a kind of light storage functional material. Long afterglow luminescent materials absorb the energy of external light sources under the excitation of light sources such as sunlight or ultraviolet rays and store them. After the excitation light source is turned off, they are released as visible light at room temperature to form long afterglow luminescence. In modern society, as a new, environmentally friendly, efficient, and energy-saving luminescent material, long afterglow luminescent material has attracted more and more attention. At present, long afterglow luminescent material has been rapidly developed and has been used in self-luminous light, special instructions, transportation signs, arts and crafts and other self-luminous product fields. In recent years, they have gradually expanded to application fields such as biomarkers, medical detection, information storage, and high-energy ray detection. As one of the key technologies for the multicolorization of long afterglow luminescent materials, the preparation and research of red long afterglow luminescent materials have been the focus of attention.

 

 

The red long afterglow luminescent material is one of the most important luminescent materials in the research of long afterglow luminescent materials. Among the three primary color long afterglow luminescent materials, the blue and green long afterglow luminescent materials are mainly doped with rare earth doped aluminates and silicate materials, and their chemical stability and luminescent properties basically meet the needs of practical applications, such as SrAl2O4Eu2 +, Dy3 + that emits green fluorescence, CaAl2O4: Eu2t, Nd +, etc. that emit blue fluorescence, its afterglow time can reach more than 10 hours. Compared with the blue and green long afterglow luminescent materials, the red long afterglow luminescent materials are far from the requirements of practical applications. Therefore, it is important to find red and NIR long afterglow luminescent materials with good performance. The existing red long afterglow luminescent materials are mainly divided into the following categories according to the matrix: sulfide series, aluminate series, silicate series, gallate series, germanate series, oxide series, phosphate, titanic acid Salt series, stannate series, sulfur oxide series and silicon-based nitride series.

Testing Methods for Long Afterglow Luminescent Materials

Compared with ordinary light-emitting materials, the long afterglow luminescent materials has a long-lasting light-emitting property. Therefore, studying the properties of long afterglow luminescent materials generally includes the following test methods:

1. Excitation Spectrum and Emission Spectrum

Excitation spectrum and emission spectrum are one of the most basic methods to study the luminescent properties of luminescent materials. Because many materials are in the state of powder or ceramic, the ions around the matrix of the luminescent material affect the properties of the luminescent center. It is a complex structure. The optical absorption determined by the reflection and diffuse reflection spectra is generally inaccurate. Therefore, the absorption spectrum is difficult to obtain.

The excitation spectrum refers to the relationship between the emission intensity of a certain emission line of the material and the excitation wavelength under the excitation of different wavelengths of the material. It reflects the effect of light-excitation materials with different wavelengths. In general, a good long afterglow luminescent material needs a strong excitation spectrum in the visible and ultraviolet regions.
The emission spectrum refers to the light intensity distribution of different wavelengths emitted by a material under a certain-specific wavelength excitation. In most cases, the emission spectrum of a material is a continuous line consisting of one or several emission peaks. The emission peak can be represented by a normal distribution.

For long afterglow luminescent materials, after the excitation light source is excited for a period of time, the excitation light source is turned off to measure the emission spectrum, which is called afterglow spectrum.

 

 

2. Brightness

Brightness is a photometric quantity, the unit is cd / m2, which indicates the lightness and darkness of the light. Brightness is a subjective quantity and is how people feel about the intensity of light. The initial brightness of the long afterglow luminescent material refers to the brightness value after the excitation light source is turned off. Generally, the minimum resolution brightness that human eyes can feel is 0.32mcd / m2.

3. Afterglow Time

Afterglow time refers to the time that the long afterglow luminescent material continues to emit light within the brightness (0.32mcd / m2) visible to the human eye after the excitation light source is turned off. Afterglow time is the main indicator for judging the pros and cons of long material afterglow performance. Generally, we study the persistence time by measuring the persistence decay curve of the material.

 

 

4. Pyroluminescence

Pyroluminescence refers to the luminous phenomenon that the energy stored in the trap which is re-released in the form of light by heating. The pyroluminescence of materials is usually studied by measuring the pyroluminescence spectrum of materials, which is also an important indicator of long afterglow luminescent materials. Long afterglow luminescence is, a type of pyroluminescence in a specific temperature range (usually room temperature). Studies have shown that the length of the afterglow time of a long afterglow luminescent material is closely related to the depth of the trap, the number of electrons in the trap, and the release rate of the electrons. Pyroelectric spectroscopy is one of the most commonly used methods to study the trap energy level of long afterglow luminescent materials. The measurement of pyroelectric spectrum can directly obtain experimental data such as the depth of the trap, the distribution of electrons in the trap energy level, and the effect of external conditions on this distribution.