Effect of size variation and gamma irradiation on thermoluminescence and photoluminescence characteristics of CaSO:Eu micro- and nanophosphors.

Microcrystalline CaSO:Eu phosphor particles prepared by the acid re-crystallization method were grinded by ball-milling method and reduced to small particles of sizes ~50 nm, 200 nm, 400 nm and 5 μm. For comparison, nanocrystalline CaSO:Eu phosphor of size ~20 nm was also prepared by chemical coprecipitation method. The recorded photoluminescence emission and excitation spectra revealed that Eu is doped in CaSO:Eu in the form of Eu and Eu in all the samples of microcrystalline and nanocrystalline powders. The samples of CaSO:Eu, with different particle sizes, were irradiated with gamma rays over a range of doses ranging from 1 Gy to 100 kGy. The results of characterization by thermoluminescence method show that the intensity of the thermoluminescence peak for a given dose of gamma-rays decreases with the decrease in the particle size of CaSO:Eu. A comparison shows that CaSO:Eu of size 50 nm exhibited linear response between the thermoluminescence peak and the gamma-ray dose in the range of 1 Gy-10 kGy. This phosphor can, therefore, be used for the measurement of gamma ray dose in medical and industrial applications. A comparative study also showed that the sensitivity of thermoluminescence to gamma ray dose for the nanophosphor prepared by the ball milling technique is better than that of the nanophosphor prepared by chemical co-precipitation method.