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

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 LiLu1−xYxSiO4:0.01Ce3+,0.01Ln3+ and LiLu1−xYxSiO4:0.01Bi3+,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 LiLu0.5Y0.5SiO4:0.01Ce3+, 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 LiLu1−xYxSiO4 and LiLu0.25Y0.75Si1−yGeyO4:0.01Bi3+ solid solutions. The TL intensity of the optimized LiLu0.25Y0.75SiO4:0.01Bi3+ 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 LiLu0.5Y0.5SiO4:0.01Ce3+,0.01Sm3+ and LiLu0.25Y0.75SiO4:0.01Bi3+ phosphors dispersed in silicone gel imaging plates.