Choose the best ending a, b, or c.
1 .Luminescence is emission of light by … a. radioactive objects b. cool objects c. hot objects 2 .Incandescent bodies are … a. in the form of lightning b. organic substances c. pigments 3. The first investigations of luminescence began with … a. an organic material b. a polymer c. a synthetic material 4. Alchemists hoped the “sunstone” would transform metals into … a. silver b. copper c. gold 5. The pronounced afterglow aroused the interest of many learned men of that period, who gave the material other names, including phosphorus, meaning… a. “light bearer” b. ” sun bearer” c. ” gold bearer” 6. In modern technology one of the most important phosphors is… a. barium sulfide b. calcium sulfide c. zinc sulfide 7 .The absorbed energy is liberated in the form of… a. light b. heat c. light and heat 8. The excitation involves only … a. the outermost electrons b. the most electrons c. the inner electrons 9. Luminescence efficiency depends on … a. the degree of transformation of excitation energy into light, b. the type of transformation of excitation energy into light, c. the size of transformation of excitation energy into light, 10. The name luminescence has been accepted for all light phenomena… a. not caused only by a rise of temperature. b. always caused by a rise of temperature c. never caused by a rise of temperature 11. The term phosphorescence means light emission caused by electronic transitions between levels… a. of different multiplicity, b. of multiple multiplicity, c. of like multiplicity, 12. Their main shortcoming is their relatively … a. good stability in light b. poor stability in light c. rare stability in light 13. Their “invisibility” of organic phosphors is due to the fact that they absorb practically … a. all visible light b. no visible light c. part of visible light 14. The practical value of luminescent materials lies in their capacity to transform … a. visible forms of energy into visible light. b. invisible forms of energy into visible light c discrete forms of energy into visible light 12. Use the text “Luminescence”to answer the following questions: 1. What is luminescence? 2. Who was the first investigator of luminescence? 3. Did the first investigations begin with synthetic or organic materials? 4. How did the first investigator obtain “sunstone”? 5. By whom were the first investigations performed? 6. Is the name phosphorus used for the chemical element only? 7. What materials are called phosphors? 8. What are the sources of luminescence? 9. What does luminescence efficiency depend on? 10. What is phosphorescence? 11. What is fluorescence? 12. Are inorganic or organic phosphors more important for practical application? 13. What does the practical value of luminescence lie in? 13. Put the jumbled sentences in the logical order to sum up the contents of the text. 1. The energy lifts the atoms of the material into an excited state, and then, because excited states are unstable, the material undergoes another transition, back to its unexcited ground state, and the absorbed energy is liberated in the form of either light or heat or both. 2. Luminescence is emission of light by certain materials when they are relatively cool. 3. The term phosphorescence means light emission caused by electronic transitions between levels of different multiplicity, 4. The first investigations (1603) of luminescence began with a synthetic material, 5. Luminescence emission occurs after an appropriate material has absorbed energy from a source such as ultraviolet or X-ray radiation, electron beams, chemical reactions, and so on. 6. The name lapis solaris, or “sunstone,” was given to the material because alchemists at first hoped it would transform metals into gold, the symbol for gold being the Sun. 7. The excitation involves only the outermost electrons orbiting around the nuclei of the atoms. 8. One of the first scientific investigations of the luminescence was performed in 1672 by Robert Boyle, an English scientist. 9. Today, the name phosphorus is used for the chemical element only, whereas certain microcrystalline luminescent materials are called phosphors. 10. In 1866 the first stable zinc sulfide phosphor was described. It is one of the most important phosphors in modern technology. 11. The practical value of luminescent materials lies in their capacity to transform invisible forms of energy into visible light. 12. Their main shortcoming is their relatively poor stability in light, because of which they are used mostly when durability is not required. 13. Although the inorganic phosphors are industrially produced in far higher quantities (several hundred tons per year) than the organic luminescent materials, some types of the latter are becoming more and more important in special fields of practical application.
v Follow-up activities 14. Choose the key sentences from the text “Luminescence” and write them down. Now work in pairs (or in groups). Ask your groupmate(s) to translate your Russian versions of the key sentences into English. Swap the roles.
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