Fabrication and ESR Characterization of Transparent CaLa2S4

The preparation of calcium lanthanum sulfide (nominally CaLa{sub 2}S{sub 4}) powder and its processing into a fully dense optical ceramic by sintering and hot isostatic pressing are described. Maximum infrared transmission is observed for the atomic ratio La/Ca = 2.7. Observation of the characteristic ESR signal of the impurity Mn{sup 2+} shows that CaS is present in the CaLa{sub 2}S{sub 4} powder. The CaS is not seen after sintering at 1,150{degree}C under 100 kPa (1 atm) of H{sub 2}S. A second cycle of hot isostatic pressing above 990{degree}C causes loss of sulfur from the ceramic, decreases the ir transmission, and introduces paramagnetic defects. Sulfur deficiency is inferred from the reduction of H{sup +} to H{sub 2} when the ceramic is dissolved in acid.