Absorption Characteristics of the Phosphate Glasses Containing Ferrous Iron Introduced as the Near Infra-red Absorbent

Preparation of alumino-phosphate glasses containing a few per cent of FeO, which are used as the infra-red shielding glass, are fairly difficult because their light absorption spectrum is liable to be affected delicately by their chemical compositions even when they are prepared under the same melting condition. The author has made a study on the effects of chemical composition on the light absorption characteristics of this type of glasses.Glasses of the two system, P2O5-Al2O3-ZnO-R2O and P2O5-Al2O3-B2O3-R2O, both containing FeO as the infra-red absorbent, were melted under the reducing condition given by the addition of metallic silicon. For the glasses prepared the absorption measurement was made in the range 0.4 to 2.2μ.For these glasses two strong absorption bands were almost always observed at about 1.1 and 2.2μ in their absorption spectrum. The glasses containing FeO more than 3.2 mole per cent and R2O less than 5 mole per cent were found to have a satisfactory infrared shielding power. With increasing the alkali (R2O) content the infra-red absorption of glass decreased, becomming liable to be affected by the kind of alkali. When the R2O content reached to 14 mole per cent, with the exception of lithia, the glasses were stained with brown color, showing the anomalous absorption at the shortwave region. The infrared absorption of the glass containing B2O3 was little stronger than that of the glass containing ZnO.The relation between the state of iron in the phosphate glasses and the absorption characteristics was explained by the screening theory proposed by W. A. Weyl.