Since ancient times, human beings have loved light and feared darkness, and dreamed of controlling light at will. Now we have developed many practical luminescent materials. Among these luminescent materials, rare earth elements play a great role, and the role of rare earth elements far exceeds that of other elements.
I. Rare Earth Luminescent Materials
The luminescence phenomenon of matter can be roughly divided into two categories: one is that the matter emits heat radiation when heated, and the other is that the object is stimulated to absorb energy, transition to the excited state (unstable state), and release energy in the form of light when returning to the ground state. Most luminescent materials with rare earth compounds and rare earth elements as activators belong to the latter category, namely rare earth phosphors. Rare earth atoms are rich in electronic energy levels, because 4f orbitals exist in the electronic configuration of rare earth atoms, which creates conditions for various energy level transitions and thus obtains various luminescent properties. Rare earth is a huge treasure house of luminescent materials, in which rare earth elements play a very important role.
Since the energy crisis occurred in the world in 1973, many countries have devoted themselves to developing energy-saving luminescent materials, so the research on making fluorescent lamps with rare earth tricolor fluorescent materials came into being. From 65438 to 0979, Philips Company of the Netherlands first successfully developed it and then put it on the market. Since then, various specifications of rare earth tricolor fluorescent lamps have come out. With the continuous improvement of human living standards, color TV sets began to develop in the direction of large screen and high definition. Rare earth phosphors show excellent properties in these aspects, thus providing an ideal luminescent material for human beings to realize large screen and high definition of color TV.
Compared with the corresponding non-rare earth fluorescent materials, rare earth fluorescent materials are superior in luminous efficiency and light color. Therefore, in recent years, the use of rare earth fluorescent materials has become more and more extensive, and the annual consumption has increased rapidly.
According to different excitation sources, rare earth luminescent materials can be divided into photoluminescence (ultraviolet or visible light excitation), cathode-ray luminescence (electron beam excitation), X-ray luminescence (X-ray excitation) and electroluminescence (electric field excitation) materials.
2. Photoluminescent material-fluorescent powder for lamps
Since luminescent materials were actually applied to lamps in the late 1970s, rare earth energy-saving fluorescent lamps and metal halide lamps have developed towards high power, miniaturization, low light attenuation, high luminous efficiency, high color rendering, no pollution, no stroboscopic, practicality, intelligence and artistry. Mainly used for various light sources, such as lighting, copier light source, photochemical light source, etc. Among them, the energy-saving lamps made of tricolor phosphors (composed of red, green and blue rare earth phosphors in a certain proportion) have attracted the attention of all countries in the world because of their light efficiency more than twice that of incandescent lamps and good light color. The improvement of the quality of rare earth luminescent materials and the development of application technology have promoted the research, production and application of a new generation of energy-saving light sources, promoted the development of many related industries, and continuously enhanced their supporting capabilities.
A typical hot cathode fluorescent lamp is a fluorescent powder coated on the inner wall of a glass tube, which emits visible light under the excitation of ultraviolet rays. When the lamp is energized, a discharge occurs between tungsten wire electrodes encapsulated at both ends of the lamp. Short-wave radiation is mainly converted into visible light by fluorescent powder and emits light. Rare earth tricolor fluorescent lamps contain rare earth phosphors of yttrium, europium and terbium, which can emit brighter light than standard fluorescent lamps and are closer to the solar spectrum. At the same time, this lamp can save 50% energy consumption. Tricolor phosphors are a mixture of three phosphors that emit narrow-band red (6 1 1 nm), green (545 nm) and blue (450 nm) spectra. The lamp tube is coated with a thin layer of halophosphate phosphor and then with a thin layer of tricolor phosphor. Each tricolor cathode fluorescent lamp contains an average of 4.5g phosphors, including 60%Eu3+ doped yttrium oxide (red powder), 30%Tb3+ activated cerium magnesium aluminate (green powder) and 10%Eu2+ activated barium magnesium aluminate (powder blue).
Rare earth activated phosphors commonly used for tricolor phosphors are:
Red powder: yttrium oxide activated by europium (Eu3+), sometimes doped with Bi3+* *.
Powder blue: Eu2+ activated silicate matrix.
Europium (Eu2+) Activated Aluminate Matrix
Europium (Eu2+) Activated Chlorophosphate Matrix
Europium (Eu2+) Activated Barium Magnesium Aluminate
Green powder: Tb3+, Bi3+ and Ce3.
+) activated magnesium aluminate
Terbium (Tb3+) and Gadolinium (Gd3+) Activated Barium Magnesium Aluminate
1. Rare earth energy-saving lamp
Rare earth phosphors are mainly used for high-performance fluorescent lamps in offices, department stores and factories. Since the mid-1980s, with the successful development of cheap fluorescent powder containing less terbium, the application of this energy-saving lamp has increased rapidly. TMT2 straight tube fluorescent lamp was introduced internationally in the mid-1990s, with a diameter of only 7mm, a power of 6W ~ 13W, a luminous efficiency of 621m/w ... T5 straight tube fluorescent lamp has a diameter of 16mm and a power of 14w ~ 35w, and the luminous efficiency of 28W fluorescent lamp can reach/kloc. A compact high-power and intense rare earth fluorescent lamp (55W ~ 120W) has been developed in China, which is suitable for outdoor lighting, and its luminous efficiency is above 801m/w. ..
A new generation of high-frequency environmental protection energy-saving lamp T5 fluorescent lamp is an ideal energy-saving lighting source. The lamp tube is characterized by coating rare earth tricolor fluorescent powder as luminous body, using solid mercury to reduce secondary pollution, and adopting new high-frequency electric lighting technology, which has high luminous efficiency, good light color and no stroboscopic, improving light quality, shortening working procedures, reducing energy consumption, reducing mercury pollution, purifying production environment and improving production efficiency. It is a product to be vigorously promoted in the next few years, and its market prospect is better than the current compact energy-saving fluorescent lamp.
In recent years, the enhanced T5 high-frequency energy-saving fluorescent tube has been introduced internationally, which improves the luminous flux per unit area and gives full play to the role of small diameter and high luminous flux.
Shanghai Dongli Lighting Appliance Co., Ltd., Jiangnan Energy Saving Lamp Factory, Huaxing Optoelectronic Industrial Company and other units have recently introduced compact energy-saving fluorescent lamps with high power, high luminous flux, high color rendering and strong light. T5 E40 and E27 lamp holders developed and produced by Huaxing Optoelectronic Industry Co., Ltd. are equivalent in size to high-pressure mercury lamps and high-pressure sodium lamps below 250W, with color rendering index ra >: 80, which are suitable for outdoor lighting.
Energy-saving lamps are an important part of green lighting project, and promoting the use of rare earth tricolor energy-saving lamps is one of the effective measures for energy conservation and environmental protection.
2. Other types of rare earth fluorescent lamps
(1) mercury lamp
Rare earth phosphors have been used in high-pressure mercury lamps for many years. The principle of this lamp is to use the discharge effect in argon and mercury vapor, and its light intensity is higher than that of fluorescent lamp. Europium-activated barium yttrium titanate phosphor can improve the light color. The main application of high-pressure mercury lamp is street and factory lighting, which requires strong white light. However, in recent years, sodium discharge lamps and metal halide HQT lamps have replaced high-pressure mercury lamps, and the market has declined. Sodium discharge lamps and metal halide HQT lamps have better color reproducibility than mercury lamps and emit natural white light. Researchers at the Massachusetts Laboratory of General Telegraph and Telephone Company have developed an improved low color temperature mercury lamp. A 400W warm-color mercury lamp is made by mixing cerium-activated barium yttrium titanate phosphors, with an illumination of 25,500 lumens and a color temperature of 3,350 K, which is more stable and efficient than ordinary mercury lamps.
(2) carbon arc lamp
Adding rare earth fluoride into the rod core increases the arc intensity to 10 times, and at the same time, the arc color changes from light yellow to recent light color. This kind of carbon arc lamp is used as searchlight and color film camera and projector.
(3) High pressure sodium lamp
Semi-transparent alumina is used as the arc tube material of high-pressure sodium lamp, and a small amount of magnesium oxide and yttrium oxide are added into alumina as sintering AIDS to improve the optical properties of the material. In order to improve the translucency of alumina, the particle size of yttrium oxide should be about 25 microns. If the particle size is too large, the strength will decrease. At present, the problem of high-pressure sodium lamp is the sodium corrosion of alumina tube caused by rare earth impurity segregation.