“…For Ho 3+ (5 mol%)‐doped thoria sample, in addition to strong absorption band at 220‐230 nm (due to ligand to metal charge transfer (LMCT) transition), additional absorptions at 361, 418, 454, 483, 538, and 642 nm from the intraconfigurational f‐f transitions of Ho 3+ ‐ion ( 4 I 8 (ground state) to 4 G 9/2 , 5 G 5 , 5 G 6 , 5 F 3 , 5 S 2 (and 5 F 4 ), and 5 F 5 (excited states)) were seen . Similarly, transitions of Er 3+ ‐ions from 4 I 15/2 (ground state) to 4 G 11/2 , 4 F 7/2 , 2 H 11/2 , 4 S 3/2 , 4 F 9/2 , 4 I 9/2 , and 4 I 11/2 (excited states) appeared at 377, 487, 519, 546, 650, 795, and 972 nm in the UV‐visible spectrum of Er 3+ ‐doped thoria sample . Similarly, from the presence of bands at 328, 470, 690, and 792 nm attributable to the transitions, 3 H 6 (ground state) to 1 D 4 , 1 G 4 , 3 F 3 , and 3 H 6 , (excited states), presence of Tm 3+ in the sample was evident .…”