Abstract:

In order to explain the reason why the phosphor LaOBr:Tb gradually loses its luminescence ability in an atmospheric condition, the action of water vapor on the matrix compound LaOBr has been investigated. The experimental methods used in this investigation were differential thermal analysis, thermal gravimetry, electroresistivity measurement, chemical analysis, infrared absorption spectrophotometry, and x-ray diffractometry. Reaction mechanism between water vapor and LaOBr has been identified as follows: LaOBr+H₂O < 160℃ LaOBr·H₂O 160℃ La(OH)₂Br The two intermediate products (activated by terbium) are nonluminescent. The finally restored LaOBr:Tb formed by the dehydration of La(OH)₂Br at 360℃ exhibits only a rather weak luminescence.Moreover several factors in the preparation process have been proved to have influence on the chemical as well as luminescent stability of terbium activated lanthanum oxybromide.