Electroluminescent radiator is a radiating semiconductor device that uses electroluminescence of electroluminescent phosphor . In the literature [1] , powder and film emitters are described.
Content
Electroluminescent Powder Emitter
The first developments of powder emitters belong to 1952 [2] .
The powder emitter is a multilayer structure, the base of which is a glass or plastic plate ( substrate ). A successively conducting transparent electrode made of metal oxides ( SnO 2 , In O 2 , CdO ), etc. is applied to the substrate, an electroluminophore layer 25–100 µm thick, a protective dielectric layer ( varnish coating or a SiO layer, SiO 2 ), an opaque metallic electrode . Zinc sulphide (ZnS) zinc selenide (ZnSe) is used as a phosphor, which is activated by impurities of copper , manganese or other elements to obtain a higher luminance brightness. Grains (polycrystals) of zinc sulfide are interconnected by dielectric materials (organic resins) with high dielectric constant . For this reason, electroluminescent powder emitters work only with alternating voltage on the electrodes (excitation voltage of 90-140 V at a frequency of 400 to 1400 Hz).
Electroluminescent Film Emitter
It differs from the powder by the presence between the electrodes of a homogeneous polycrystalline film of an electroluminophor with a thickness of about 0.2 μm, which is created by thermal evaporation with deposition in a vacuum. Since there is no dielectric in the electroluminor, the film emitters can operate at a constant current. Compared with powder emitters, the operating voltage of film emitters is much less (20-30 V). Activating the phosphor with rare-earth fluoride materials allows you to increase light output and brightness, as well as change the color of the glow.
In 1974, a three-layer film emitter with two insulating films ( Y 2 O 3 and Si 3 N 4 ) with high dielectric constant was developed [2] .
Electroluminescent film emitters are inferior to powder emitters in terms of economy and service life.
Basic parameters
- Effective brightness - the brightness of the glow at a certain frequency of alternating voltage (for powder) and at a certain value of this voltage or current density.
- Brightness characteristic - the dependence of the brightness of the glow from the voltage on the radiator. A large non-linearity characteristic is used when creating matrix screens to enhance image contrast. Film emitters allow you to get higher contrast and resolution compared to powder.
- The multiplicity of changes in brightness - characterizes the steepness of the luminance characteristic when the voltage on the radiator changes twice. The multiplicity of changes in the brightness of powder emitters does not exceed 25, for film - up to 1000 [1] .
- The dependence of the effective brightness on the frequency (for powder emitters).
- The spectrum of the emitted light (glow color) determined by the activators added to the phosphor.
Features and Applications
Electroluminescent film and powder emitters are characterized by a large scatter of parameters, which is their disadvantage.
The brightness of the emitters is significantly reduced during operation. A decrease in brightness over 1000–5000 hours of operation can occur 2-3 times [3] .
But this refers to electroluminophors of the first generation with particle sizes above 30 nm, recent studies in this area allowed the creation of electroluminophores with sizes of 12-18 nm, respectively, which made it possible to improve the operating performance of the luminance brightness up to 300 cd, and the “drawdown” in brightness is observed in the first 20— 40 hours of operation up to 20% that is regulated by the output parameters of the inverter in the future, the period of constant luminescence reaches 12,000 hours.
The brightness of the glow depends on the frequency and voltage of the excitation and increases with their growth [3] .
Depending on the design of an opaque electrode, electroluminescent emitters can display alphabetic, numeric, symbolic information and build matrix screens based on them.
See also
- Electroluminescent display
- Electroluminescent wire
- Electroluminescent panel
- Light-emitting diode
- Semiconductor materials
- Electronic indicator
Notes
- ↑ 1 2 Pasynkov V.V., Chirkin L.K. Semiconductor devices: A textbook for universities. - 4th pererabot. and add. ed. - M .: Higher School, 1987. - p. 370-373. - 479 s. - 50 000 copies
- ↑ 1 2 Bystrov Yu. A., Litvak I. I., Persianov G. M. Electronic devices for displaying information. - M .: Radio and communication, 1985 pages =. - 240 s. - 18 000 copies
- ↑ 1 2 Ivanov V. I., Aksenov A. I., Yushin A. M. Semiconductor optoelectronic devices: A Handbook / Edited by N. N. Goryunova. - M .: Energoatomizdat, 1984. - 184 p. - 150 000 copies
Literature
- Pasynkov V.V., Chirkin L.K. Semiconductor devices: A textbook for universities. - 4th pererabot. and add. ed. - M .: Higher School, 1987. - p. 370-373. - 479 s. - 50 000 copies
- Ivanov V.I., Aksenov A.I., Yushin A.M. Semiconductor optoelectronic devices: Handbook / Ed. N. N. Goryunova. - M .: Energoatomizdat, 1984. - 184 p. - 150 000 copies
- Bystrov Yu. A., Litvak I. I., Persianov G. M. Electronic devices for displaying information. - M .: Radio and communication, 1985. - 240 p. - 18 000 copies