How is Luminous Powder Produced?

Many people are fascinated by the luminous properties of glow in the dark powder, but few understand its manufacturing process. Here, we’ll demystify its production and explore how it’s “created” step by step.

Historical Evolution: Three Generations of Glow in the Dark Powder

The glowing mechanism of glow-in-the-dark powder has undergone several innovations, evolving from dangerous radioactive materials to today’s safe and eco- friendly products. Each iteration marks a significant advancement in technology.

  • First Generation Glow-in-the-Dark Powder

First-generation glow-in-the-dark powder wasn’t actually a powder; it was primarily a natural mineral. Its inherent luminescence properties stemmed from the element Radium, which is highly radioactive and poses a serious health risk. Therefore this type of glow-in-the-dark material was not commercially viable.

  • Second Generation Glow-in-the-Dark Powder

Second-generation glow-in-the-dark powder uses Zinc Sulfide as its raw material and activators such as Copper and Cobalt to generate its light. All of these elements are non-radioactive. It is a significant step forward in safety. However, Zinc Sulfide-based glow-in-the-dark powders contain Sulfur. The emissions generated during its production process will pollute the environment, leading to acid rain and acidic water, which in turn accelerates the corrosion of buildings, damages soil structure, and so on. Furthermore, this kind of glow in the dark powder is chemically unstable, susceptible to moisture and aging, and have poor weather resistance, which limiting the application. The short glow duration (<30 minutes) also fails to meet the growing market demand for long-lasting glow.

  • Third-Generation Glow-in-the-Dark Powders

The vast majority of products on the market today belong to the third generation, primarily composed of Strontium Aluminate, typically activated by the rare earth elements dysprosium (Dy³⁺) and europium (Eu²⁺). This is considered a major breakthrough in the development of glow-in-the-dark powder.

Not only does the entire production process eliminate pollutants, the product itself is non-toxic, non-radiation, safe, and eco-friendly. Furthermore, after sufficient illumination, it maintains a persistent glow for 8-12 hours in complete darkness, meeting the long-lasting glow requirements for applications such as emergency signs, directional markers, and landscapes. It also exhibits extremely stable chemical properties, especially after waterproof coating treatment, maintaining long-term performance (effective for 15-20 years). It is particularly suitable for water-based media (such as water-based paints and inks). This type of luminescent powder is currently widely used in safety signages, toys, clothing, household items, architectural decoration, and other fields.

Production Process of The Third Generation – Strontium Aluminate Luminous Powder: Raw Materials and Rare Earth Activators:

Strontium Aluminate luminescent powder is made mainly from Strontium Carbonate and Aluminum Oxide. The purity and particle size stability of these raw materials are important factors affecting the brightness and also the size of the luminescent powder. High-purity raw materials ensure a more perfect crystal structure and fewer impurities. And impurities may reduce luminous efficiency and ultimately affecting the brightness and duration of the luminescent powder.

Strontium Aluminate luminescent powder’s luminescence is primarily achieved by incorporating rare earth elements, particularly Dysprosium (Dy³⁺) and Europium (Eu²⁺), as activators. The precise ratio of these elements is one of the core technologies of glow-in-the-dark powder. These ratios directly affect the powder’s performance such as brightness, afterglow duration, and color of the glow-in-the-dark powder etc. Different manufacturers will adjust the formulations based on their own technologies.

Production Process:

The production process of glow-in-the-dark powder is highly sophisticated, requiring rigorous control at every stage to ensure the final product’s luminous performance, stability, and application suitability. The entire process consists of the following six steps:

Production Process Flow Chart

1. Mixing

Mixing involves combining basic raw materials, including inorganic compounds such as Strontium Carbonate (SrCO₃) and Aluminum Oxide (Al₂O₃), with a specific amount of Europium (Eu²⁺) and Dysprosium (Dy³⁺). ​​These raw materials must be rigorously dried, weighed, and mixed to ensure precise proportions. Even slight deviations can result in variations in brightness, afterglow duration, or color. High-speed mixing equipments are typically used during the mixing process to ensure uniform mixing of the raw materials. Therefore, this step directly determines the fundamental performance of the powder.

2. Heating

The mixed raw materials are then heated in a high-temperature, enclosed kiln. After a period of reductive calcination (typically reaching temperatures as high as 1450°C), a complex chemical reaction occurs between the various raw materials, forming a new substance—Strontium Aluminate (SrAl₂O₄). Its physical form also transforms from powder to large lumps, which is the key to the properties of the luminescent powder. Kilns generally adopt tunnel kilns, roller kilns, or high-temperature electric furnaces. Reductive calcination must be completed under a precise temperature curve to avoid problems such as uneven crystals, color deviation, and luminescence attenuation.

3. Crushing and Milling

The calcined Strontium Aluminate lumps require physical crushing. First, a crusher is used to pulverize them into medium-sized particles, which are then ground in a ball mill. In the ball mill, wear-resistant Zirconium Oxide or Aluminum Oxide balls rotate at high speed, repeatedly impacting and grinding the particles, gradually reducing them to a relatively uniform fine powder. Controlling the grinding time and speed is important. Over-grinding can damage the crystal structure and reduce luminescence brightness, while insufficient grinding can result in coarse particles.

4. Sieving

The ground powder needs to be graded using sieving equipments.

For normal luminous powders, they are separated by precision sieves, yielding products ranging from tens to hundreds of microns, suitable for applications in coatings, plastics, inks, silicons, glasses, ceramics and etc. However, for ultra-fine luminous powders (2-15μm), traditional sieving processes are inadequate. These products often require airflow classification, centrifugal separation, or wet separation to obtain finer and more uniform particles to meet the demands of ultra-thin coatings or ultra-fine diameter products, which require extremely high fineness. Each manufacturer uses different separation technologies based on their production conditions and product characteristics.

5. Testing

Testing luminous powder is particularly important, as customers often lack professional testing capabilities and rely more on visual inspection to determine the product’s luminescence effect. Therefore, ensuring the stability of luminous powder through scientific and standardized testing is a key concern for luminous powder suppliers.

The core testing items for glow-in-the-dark powder mainly include two aspects: particle size and its distribution range, as well as brightness and afterglow duration. These two factors fundamentally determine the performance of glow-in-the-dark powder, from production to end-use.

The testing of glow-in-the-dark powder differs significantly from that of ordinary products. This is because test results are significantly affected by factors such as the accuracy of the testing equipment, testing standards, environmental conditions, and the stringency of process controls.

  • Impact of testing equipment:

(1) Particle size and distribution: Commonly used testing equipments include electron microscopes and laser particle size analyzers. Particle size directly affects the stability and efficiency of the production process, and particle size distribution determines the suitability of glow-in-the-dark powder for specific applications, such as ultra-thin coatings. Higher-precision equipment captures particles with greater accuracy, more accurately reflecting the actual particle size of the glow-in-the-dark powder.

(2) Brightness and afterglow time: These are typically assessed using an illuminometer or luminance meter. Higher-precision testing equipment has a narrower margin of error and greater stability over repeated tests.

  • Impact of testing standards:

Take the charging light as an example. Different charging light types, brightness, and exposure times can lead to significant variations in brightness data. In luminescence industry, the most widely used standard is the European DIN 67510 (specifying a D65 light source, 1000 lux illumination, and a 5-minute exposure time). However, some suppliers use different testing conditions. Therefore, when referencing and comparing data, it is important to first clarify the standards used to avoid mis-judgments due to inconsistent standards.

  • Impact of the testing environment:

The testing environment for glow powder primarily includes ambient brightness, temperature, and humidity.

The afterglow brightness must be tested in a completely darkroom. The presence of stray light or background light can increase the brightness data. Ambient temperature and humidity can also affect the light absorption and emission of glow powder, leading to data deviations.

  • Impact of testing process control:

Strict process control can minimize human interference. This involves multiple steps, such as sample preparation (thickness, dosage, coating uniformity), the distance and exposure time of the excitation light source, instrument calibration, and operating procedures. Even the slightest deviation can lead to significant data deviations due to excessive or insufficient light absorption in the sample being tested. Therefore, the use of automated testing equipment, the establishment of strict standardized operating procedures, and rigorous operator training are crucial to ensure scientific and comparable test results.

6. Packaging and Stocking

Finally, qualified products that pass all tests are packaged according to customer specifications for easy transportation and distribution.

Customers often wonder: What exactly differentiates products from different suppliers? Our recommendation is to verify this with product samples. The reason is that manufacturers vary significantly in every aspects such as formulation, production technology, manufacturing equipment, testing controll, and even the expertise of their technical teams. All of these differences across the entire production will ultimately lead to distinct performances in the final products. Therefore, verifying via samples is the best way to confirm whether a product meets specific needs.