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Phosphors - preparation, composition

Phosphors are solids which after irradiation by daylight or UV radiation passes into the excited state, and returns slowly to the ground state by the emission of secondary radiation, often visible to the naked eye and observed as a flicker luminescence. The chemical nature are typically sulfides elements II. A group, especially Ca, Sr, activated by trace impurities of other rare elements (Bi, Mn, Ba, and Cu). Other types of phosphors are based on the basi tungstates of calcium (near mineral wolframite) or zinc sulphide (called blejno Sidotovo).

Phosphors are prepared by high-temperature synthesis from air. The composition of the mixture, which after annealing provide phosphors seem to be found purely empirically, not for them a satisfactory theoretical explanation. Color phosphor is mainly determined by the type and amounts of additives basic sulfide.

The first mention of the phosphors are from Italy (author unknown), and these substances have been referred to as the Bologna phosphorus. The other compositions are particularly worthy of Vanino and KA Hoffman.

Light blue phosphors

Chemicals: calcium hydroxide, strontium carbonate, sulfur (flowers of sulfur), anhydrous sodium sulphate, potassium sulphate, lithium carbonate, 1% aqueous solution of rubidium nitrate, a suspension of 0.05 g bismuth nitrate in 10 ml of ethanol

All chemicals should be pure p.a.!

The following regulations are working with a very good purity chemicals (pa). Careful work, weighing, transport components (ie, the so-called small cmrndací factor) are a prerequisite for success.

The porcelain boat gradually navážíme with an accuracy of at least two decimal places, 1.30 g of calcium hydroxide, strontium carbonate, 1.00 grams, 0.30 grams of sulfur in the form of sulfur flower, 0.05 g of anhydrous sodium sulphate , 0.05 g of potassium sulphate, 0.10 g of lithium carbonate. Components quantitatively to the mortar, which is spread on a fine homogeneous powder. Pay attention to the spreading avoid spilling the powder bowl.

The powder in the bowl, add 0.1 ml of 1% aqueous solution of rubidium nitrate and 0.1 ml of a suspension of 0.05 g bismuth nitrate in 10 ml of ethanol (metered syringe from a thin needle. Amount of bismuth in mixture strongly affects the color of light emitted luminescence decay length of the prepared phosphors. should be strictly observed volume of the suspension. The more bismuth was used, the emitted light is darker blue and the shorter the time of extinction phosphor). Added solutions will form on the surface of the mixture droplets. Gently rocking the mortar arrange to drop wrapped powder mixture, going for solid balls. Only then spoon mixture again. Perfectly homogeneous mixture into the annealing crucible and copyist mix thoroughly compacted. On the surface of the mixture add 1 g of starch (3 small spoons), which extends in the annealing and decomposition products protect the phosphor against air oxidation.

crucible placed in a fume hood in the triangle, crucible cover with a lid or higher annealing crucible so as not to mix with air. The mixture is annealed 10 minutes luminous flame burner propanbutanového (tempering crucible), then strongly calcined nesvítivým burner flame for 30 minutes so that the crucible into glowed orange glow. Then let cool 5 minutes in glowing flame burner and heating propanbutanového interrupted.

From the cooled crucible remove the top layer of charred starch, under which it is formed phosphor vr form of sintered stones, isolating, mechanically clean the residue from carbon. Peck crush into powder and store in a dry prachovnici (phosphor readily hydrolyzed to form toxic hydrogen sulphide).

mixture II - colorless light

Simple luminous material to prepare a mixture of 20 g of calcium oxide, 6 g bolt sulfur, 2 g of starch, 0.5 g of potassium sulphate, 0.5 g sodium sulfate (anhydrous) and 2 ml 0.5 g bismuth nitrate in 100 ml of ethanol, to which we add a few drops of conc. nitric acid. Homogeneous mixture hang of a porcelain crucible and annealed 45 minutes a gas burner or better in an electric furnace.

mixture III - purple shining

60 g of strontium thiosulfate (I understand that these chemicals San poorly, I saw a double entry solution reaction of strontium perchlorate with potassium thiosulfate thiosulfate strintnatý has formed at 0 ° C 10 times greater than the solubility of potassium perchlorate - see zipped excel file .), 2 ml bismuth nitrate solution (0.5% alcohol solution), 6 ml uranyl nitrate solution (0.5% alcohol solution). Thoroughly homogenized, ethanol evaporated and the mixture heated in a porcelain crucible closed with 45 minutes using torches or furnace at 1000-1200 ° C.

mixture IV - Yellow on

100 g of strontium carbonate, 100 g of sulfur, 0.5 g KCl, 0.5 g NaCl, 0.4 g of manganese chloride. The homogenous mixture is annealed for 45 minutes at 1000 to 1200 ° C in a porcelain crucible with a lid.

mixture V - red light

40 g of barium carbonate, 6 g of sulfur, 1 g of lithium carbonate, 0.02 g of sodium carbonate, 0.47 g rubidium carbonate. The homogenous mixture is annealed for 45 minutes at 1000 to 1200 ° C in a porcelain crucible with a lid.

mixture VI

20 g of calcium oxide, 4 g of potassium sulfate, 20 g bolt sulfur, 1.5 ml bismuth nitrate solution (1% ethanolic solution), 0.6 ml of sodium nitrate thóričitého (1% solution in distilled water) and 4 g of starch. Homogeneous and dried mixture is annealed for 45 minutes at 1000 to 1200 ° C in a porcelain crucible with a lid.

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