POWDER LUMINESCENT MATERIALS

At the Volga Research and Development Institute in Saratov, powder phosphors are developed for use in vacuum fluorescent displays (VFDs) produced by the neighboring company Reflector. The goals for R&D are to develop low voltage phosphors in the range of 4-20 V for color displays. Volga develops phosphors that are then mass-produced in Stavropol. The Volga laboratories include a lab to develop specialized phosphors, indium-tin-oxide evaporation equipment, and reactive plasma etching equipment. For phosphor development, the emphasis is on low-voltage materials using ZnO for green, Cd:ZnS for red, and ZnS for blue. For 200-300 V applications, ZnS is used for green and blue, and Y-oxide for red (TV analog materials). The screen processing methods used are silk-screening and electrophoretic deposition. The ZnO for green has a brightness of 10-12 lm/W. Using silk- screening techniques, lines of 100-150 mm thick of phosphor have been deposited. Volga's scientists are studying ZnS and ZnO for FEDs. Some work has been done on thick-film (10 mm) Zn sulfides and oxides, but there has been no thin-film materials work.

Reflector in Saratov obtained patents on phosphors and device structures for low- voltage VFDs that it manufactures. The phosphors are mass-produced at Russia's main phosphor production enterprise, Luminophor in Stavropol. Reflector and the Volga Institute developed a red, green, and blue multicolor VFD production process. Production modules include glass substrate cleaning, phosphor screen printing, and carbon coating and screening. Reflector claims several technical advantages for its VFD, including the low voltage structure that provides very high brightness, high lifetime (approx. 100,000 hrs), and multicolor capability.

In Fryazino, Platan develops and produces the powder phosphors used in its products, CRTs and CRT projection systems. The phosphor facility is large and well-equipped. The company's scientists are working on low-voltage phosphors and multicomponent phosphors that emit different colors depending on the beam voltage or current. The company claims it has a 10 V phosphor; a 30 V phosphor was demonstrated. One phosphor screen, a material doped with Eu, showed strong evidence of laser action; that is, it exhibited threshold-like intensity behavior with significant spectral narrowing. Platan has developed a line of CRTs that uses the color-modulated phosphors. The voltage- induced color shift was sufficient to produce five distinct hues, and the colors were used to color-code targets and write symbology in a large (approx. 30") tube. Dr. Saschin at the phosphor lab showed phosphor encapsulated in polyethylene/polypropylene for converting UV radiation to 610-700 nm, used to enhance plant growth and to warm enclosures. Phosphors are mass-produced at factories in Kustova and Dorogomilovsky.

In the Department of Physical and Colloidal Chemistry at L'viv State University, Ukraine, Professors M.S. Pidzyrailo and M.M. Soltys discussed R&D on cathodoluminescent screens based on three kinds of phosphor powders (425, 450, and 540 nm). The following materials (1-4 micron diameter powders) with small crystal grains are typically used: ZnS:Ag, Y3Al5O12:Ce, and Y2SiO5:Ce. L'viv's collaboration with Erotron has resulted in highly informative displays with 60 micron lines. The screen operates in a two-color mode (red and green); the threshold of the color switching is 5-10 kV. Dr. V.D. Bondar in the Laboratory of Physical Electronics performs R&D on the luminescent screens. The screen is composed of two luminescent films possessing different colors (e.g., red Y2O2S:Eu). The color of luminescence depends on the intensity of the electron beam that defines its penetration depth.

In the Department of Optoelectronics at the Institute of Semiconductors, Ukraine Academy of Sciences, the characterization and testing of powder-luminescent indicators and screens is done rather than research. At the time of the WTEC visit, the scientists were testing a relatively large screen that was manufactured in Mukachevo (West Ukraine), but its performance was poor.


Published: December 1994; WTEC Hyper-Librarian