Towards information storage by designing both electron and hole detrapping processes in bismuth and lanthanide-doped LiRE(Si,Ge)O&lt;sub&gt;4&lt;/sub&gt; (RE = Y, Lu) with high charge carrier storage capacity

Lyu, T.; Dorenbos, P.

doi:10.1016/j.cej.2020.124776

Towards information storage by designing both electron and hole detrapping processes in bismuth and lanthanide-doped LiRE(Si,Ge)O₄ (RE = Y, Lu) with high charge carrier storage capacity

Title

Towards information storage by designing both electron and hole detrapping processes in bismuth and lanthanide-doped LiRE(Si,Ge)O₄ (RE = Y, Lu) with high charge carrier storage capacity

Author

Lyu, T. (TU Delft RST/Luminescence Materials)
Dorenbos, P. (TU Delft RST/Luminescence Materials)

Date

2020

Abstract

Guided by vacuum referred binding energy (VRBE) diagrams, both the trapping and detrapping processes of electrons and holes are explored in the bismuth and lanthanide-doped LiRE(Si,Ge)O₄ (RE = Y, Lu) family of compounds. The Tm³⁺ electron trap has been combined with the deep hole traps of Ln³⁺ (Ln = Ce, Tb, or Pr) or Bi³⁺ in LiLuSiO₄. During the thermoluminescence readout, the electrons released from Tm²⁺ recombine with holes at Ln⁴⁺ and Bi⁴⁺ to produce typical Ln³⁺ 4f-4f or 5d-4f emission and Bi³⁺ A-band emission. The electron trap depth of lanthanide ions can be tuned by the choice of Ln³⁺ (Ln = Tm or Sm), and for fixed pair of Ln³⁺ and/or Bi³⁺ dopants like in LiLu_1−xY_xSiO₄:0.01Ce³⁺,0.01Ln³⁺ and LiLu_1−xY_xSiO₄:0.01Bi³⁺,0.01Sm³⁺ solid solutions, by adjusting x, resulting in the engineering of the VRBE at the conduction band bottom. The thermoluminescence (TL) intensity of the optimized LiLu_0.5Y_0.5SiO₄:0.01Ce³⁺, 0.005Sm³⁺ is about 8.5 times higher than that of the commercial X-ray BaFBr(I):Eu²⁺ storage phosphor. By combining deep Eu³⁺ or Bi³⁺ electron traps with Ln³⁺ (Ln = Tb or Pr) or Bi³⁺, Ln³⁺ and Bi³⁺ appear to act as less deep hole capturing centres in LiLuSiO₄. Here the recombination is achieved through hole liberation rather than the more commonly reported electron liberation. The holes are released from Ln⁴⁺ and Bi⁴⁺ to recombine with electrons at Eu²⁺ or Bi²⁺ to give characteristic Eu³⁺ 4f-4f and Bi³⁺ A-band emissions. The tailoring of Ln³⁺ and Bi³⁺ hole trap depths by crystal composition modulation is discussed in LiLu_1−xY_xSiO₄ and LiLu_0.25Y_0.75Si_1−yGe_yO₄:0.01Bi³⁺ solid solutions. The TL intensity of the optimized LiLu_0.25Y_0.75SiO₄:0.01Bi³⁺ is ~4.4 times higher than that of the commercial BaFBr(I):Eu²⁺. Proof-of-concept information storage will be demonstrated with X-ray or UV-light charged LiLu_0.5Y_0.5SiO₄:0.01Ce³⁺,0.01Sm³⁺ and LiLu_0.25Y_0.75SiO₄:0.01Bi³⁺ phosphors dispersed in silicone gel imaging plates.