Feasibility study of rare earth semiconductor lasers of the type Y2HfS5

The possibility of making a rare earth or rare earth doped semiconductor laser is investigated. The material examined in detail is Y2HfS5, which is of the general class of materials Ln2TX5, where Ln is a rare earth, T is zirconium or hafnium, and X is sulfur or selenium. For Y2HfS5;Nd, the Stark split energy levels of Nd(3+) are determined in the energy range 0 to 2 eV (the band gap of Y2HfS5). The individual line to line transition probabilities are calculated assuming S4 symmetry for the Nd(3+) site, and the branching ratios are given. The calculated branching ratio for spontaneous emission of the 4F (3/2) to the 4I (1/2) is 0.574, and the next largest branching ratio of the 4F (3/2) to 4I (9/2) is 0.298. The branching ratio for the 4I (1/2) is larger in this material than the calculated branching ratio for Nd in YAG, which is 0.480. The transition probabilities are used to calculate the excitation of the various multiplets by conduction electrons.