Manganese agglomeration and radiation damage in doped Li2B4O7

Manganese clustering effects were studied in Li2B4O7 (LTB) ceramics. The samples LTB:Me + Mn (Me = Sn, Cu, Mn, Zn, Be) were prepared by a two-stage doping method (except for LTB doped with Mn solely). EPR, pulsed cathodoluminescence, thermoluminescence (TL) were measured. Mn clustering causes supralinearity of the material response to the radiation dose, reversible shift of the dosimetric TL peak, and irreversible radiation damage. Radiation damage of the LTB crystal lattice is accompanied with the formation of a peroxide bridge instead of a single oxygen at the common vertex of two BO4 tetrahedra. Repelled by an excessive positive charge of a Mn cluster, holes are localized around at traps including the peroxide bridges where they are stable up to 630 K. The extent of the radiation damage can be estimated by the intensity of the high-temperature TL at 630 K, when the released holes recombine with the electrons near regular Mn2+. The most stable against the radiation damage and also suitable for TL dosimetry is LTB:Sn + Mn. © 201

Manganese agglomeration and radiation damage in doped Li₂B₄O₇

Manganese clustering effects were studied in Li2B4O7 (LTB) ceramics. The samples LTB:Me + Mn (Me = Sn, Cu, Mn, Zn, Be) were prepared by a two-stage doping method (except for LTB doped with Mn solely). EPR, pulsed cathodoluminescence, thermoluminescence (TL) were measured. Mn clustering causes supralinearity of the material response to the radiation dose, reversible shift of the dosimetric TL peak, and irreversible radiation damage. Radiation damage of the LTB crystal lattice is accompanied with the formation of a peroxide bridge instead of a single oxygen at the common vertex of two BO4 tetrahedra. Repelled by an excessive positive charge of a Mn cluster, holes are localized around at traps including the peroxide bridges where they are stable up to 630 K. The extent of the radiation damage can be estimated by the intensity of the high-temperature TL at 630 K, when the released holes recombine with the electrons near regular Mn2+. The most stable against the radiation damage and also suitable for TL dosimetry is LTB:Sn + Mn

Ultrafast and slow luminescence decays at energy transfer from impurity-bound excitons

Different types of ultrafast radiative transitions are considered. The most interesting among them is the case when the radiative transition is accelerated by the configurational transformation of a structural unit where it occurs. Impurity-induced VUV excitation bands of doped Li2B4O7 are attributed to the creation of impurity-bound excitons. When Mn2+ is involved into exciton recombination, the radiative transition in the Mn2+ 3d5 configuration is accelerated and occurs on a sub-nanosecond time scale. Excitation within the UV bands is connected with energy transfer from the structural units formed by the sensitizers (Cu, Sn) and oxygen to Mn2+. In this case, Mn2+ transitions are not accelerated since its excited state appears after complete relaxation of excitation in the corresponding sensitizer’s unit. Pulsed cathodoluminescence decays are rather slow due to very slow transport of electron–hole pairs and excitons in Li2B4O7