28.

K.W. Krämer, H.U. Güdel, and R.N. Schwartz
Infrared-to-visible upconversion in LaCl3 : 1% Er³⁺. Energy-level and line-strength calculations
Phys. Rev. B 56 (1997) 13830 – 13840.

29.

P. Dorenbos, J.C. van't Spijker, O.W.V. Frijns, C.W.E. van Eijk, K. Krämer, H.U. Güdel, and A. Ellens
Scintillation properties of RbGd2Br7 : Ce³⁺ crystals; fast efficient, and high density scintillators
Nucl. Instr. Meth. Phys. Res. B 132 (1997) 728 – 731.