 In recent years it has been demonstrated that nanocrystalline <unk> : Sm3 + as prepared by a co @-@ precipitation can serve as a very efficient x @-@ ray storage phosphor . The co @-@ precipitation leads to <unk> of the order of 100 @-@ 200 nm in size and their sensitivity as x @-@ ray storage phosphors is increased an astounding ∼ 500 @,@ 000 times because of the specific arrangements and density of defect centres in comparison with microcrystalline samples prepared by sintering at high temperature . The mechanism is based on the reduction of Sm3 + to Sm2 + by trapping electrons that are created upon exposure to ionizing radiation in the <unk> host . The 5 DJ @-@ 7 FJ f @-@ f luminescence lines can be very efficiently excited via the parity allowed <unk> → <unk> 5d transition at around 417 nm . The latter wavelength is ideal for efficient excitation by blue @-@ violet laser diodes as the transition is electric dipole allowed and thus relatively intense ( 400 l / ( mol ⋅ cm ) ) . The phosphor has potential applications in personal dosimetry , dosimetry and imaging in radiotherapy , and medical imaging . 
