Abstract: The paper introduces the long after glow phosphorescence material
Key words: long after glow, ZnS.
How to define a luminescent substance it? Suitable materials absorb radiation energy , and then the light is emitted , the emitted photon energy is lower than energy of the excitation radiation. This behavior has a light-emitting substance called luminescent substances. According to the excitation can be divided into different photoluminescent material , a cathode ray emitting material , an electroluminescent material , a chemiluminescent material , etc. . This article deals with photoluminescent materials are long-lasting light-emitting materials , commonly known as luminous materials.
1866 French Sidot finished first ZnS: Cu preparation , the earliest research work carried out in this series afterglow luminescent materials . Until the early 20th century, photoluminescent true realization of industrial production , but also since then, always the ZnS series dominated afterglow luminescent materials industry . To the 1990s , people began to discover and concern afterglow luminescent material has good performance and unique characteristics of the rare earth ion doped afterglow , and ushered in a maturing super long afterglow materials research and application of a new era. In recent years, the rare earth ion doped materials have been widely used in the afterglow instrument display panel and other areas concealed lighting and emergency lighting, aviation, marine and automotive , it was the rare earth ion doped materials used in the preparation of ceramic afterglow .
Long-lasting mechanism of a light-emitting and light-emitting materials
After stimulated light materials continue to issue stop is called afterglow . Called afterglow afterglow afterglow duration time of less than 1 μs is called ultrashort afterglow called short afterglow ,1-10μs inter called 10μs-1ms between short afterglow called ,1-100ms between the afterglow , called the afterglow between 100ms-1s , more than 1s is called super- long afterglow . Long afterglow luminescent material present development mechanism is not perfect, are hundreds of gongs state. The specific mechanism is as follows : After activating agent ( donor ) are incorporated into the matrix , formed in the band gap near the location of the conduction band of a series of impurity levels , the role of the trap from the conduction band movement electrons, it is likely to stay in the trap for a long time , only in the external force will not be released ; under excitation photon , electron transitions from the ground state to the excited activator state ( process 1 ) ; If the electronic ground state level that is returned directly generate transient luminous phenomena ( process 2 ) is the fluorescence emission ; optical excitation will make some electronic transitions to the conduction band ( process 3 ) , and confined in the trap ( procedure 4 ) ; If you are in the trap energy level of electrons get enough energy e, they will released from the trap (process 5 ) , which is that they may be re- captured by the trap , it may transition to the ground state activator ( process 6 ) through the conduction band , and the light emission center complex , i.e., causing long afterglow luminescent .
The persistence length and the trapping of electrons by the number N and the energy of these electrons gain on E : N , the more long afterglow time ; E within a certain range , the more long afterglow time , but can reach the trap value of the electronic release of all is that it will not help extend the afterglow of time.
Long afterglow luminescent material is divided into self-luminous type photoluminescent afterglow luminescent materials and energy storage . The former is called a permanent light emitting material , it does not need the help of any external energy for excitation emitted by the radioisotope itself containing the particles in the excitation decay due radioisotope emitted particles is uninterrupted , uniform , stable , so self-luminous materials can be sustained, steady light, its half-life decay time depends contained radioisotopes . Initially the use of natural radioactive elements α particle excitation , and later using synthetic β -type emission elements to improve the afterglow of a performance and reduce radiation damage . Latter refers to the people , such as sunlight or ultraviolet light irradiation short time after the light turned off , still can be sustained for a long time luminous materials.
Long-lasting material doped with rare earth ions
With the social and economic development, human lifestyles are undergoing tremendous changes , such as the centralization of human activities, nightlife extension , increasing the underground construction and high-rise buildings , while people also enhance awareness of security risks . Once earthquakes, fires and other unexpected disaster, how to ensure the safe evacuation of people in the shortest time , that evacuation signs of how the system can most effectively play a role , which is relevant technical experts around the world dedicated to study and solve major issues . In the conventional ZnS represented since the light emitting long afterglow luminescent material short time, low brightness, poor lightfastness shortcomings make it in practice Discard the dilemma . Developed in the 1990s, rare earth aluminate , silicate luminescent material , non-toxic , non-radioactive , chemical stability , and its luminance and continuous lighting time is 30 to 50 times ZnS as the representative of the traditional fluorescent material , and unlimited repeatedly. This efficient photoluminescent green as a precondition to self-luminous material inventions , marks the third time since the arrival of the light-emitting materials revolution. In recent years, the luminescent materials and products were quickly accepted , the amount annually.
At present , domestic and foreign carriers using photoluminescent material fire safety evacuation signs of a thin aluminum sheet products ( printed luminescent material on which a pattern ) , plastics, rubber , ink, paint, etc. After processing at room temperature or a lower temperature materials can be finalized . Compared with the several materials, ceramic materials with high strength, weather resistance , heat fire-resistant, water-resistant, easy to clean surface , tastefully decorated , long life and other advantages. At present, China ‘s ceramic decorative brick production has reached more than one billion l0 m2, is widely used in all kinds of walls, floors and pavement decoration . The advantage of the advantages of phosphorescent material and ceramic materials ceramic products rolled into one that gives luminescent features that make more extensive use of ceramic products , performance luminescent material products are also more favorable .
Therefore , long afterglow luminescent type ceramic become a hot topic all the scholars , after experimental studies heresy of time, has had promising results go .
Liu Quansheng and other high-temperature solid phase prepared SrAl2O4: Eu2 +, Dy3 +, CaAl2O4: Eu2 +, Nd3 +, CaTiO3: Pr3 + long afterglow luminescent materials , zinc borosilicate system based glazes on ceramic substrate , prepared colorful colorful pattern afterglow content luminescent ceramic glaze ceramic luminescent material was 25% ; ceramic firing temperature of 800 ℃.
Zhang Xiyan , Lully equality SrAl2O4: Eu2 +, Dy3 + luminescence ceramics in 1250 ~ 1450 ℃ to monoclinic crystal. 1400 ℃ sintered samples 4h glows bright green. Samples high strength, good chemical stability. Is the center wavelength of the emission spectrum of the broadband spectrum of 520nm , the excitation spectrum is located between 240 ~ 420nm. 10h -emitting continuous luminance of 2.15 mcd / m2, far higher than the human eye can distinguish brightness 0.32mcd/m2 minimum luminous decay curves conform I = At-n, the first 5 min, n = 0.6;. 5 to 40min, n = 1.0; 40 to 600min, n = 1.3 show that the luminescent ceramic afterglow luminance variation with time is longer decay slower .