The results of a series of pump–probe spectral hole-burning experiments are presented on Yb³⁺- or Er³⁺-doped Li₆Y(BO₃)₃ (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole has a complex structure for Yb³⁺ with superposed narrow and broad bands, while a single absorption hole has been observed for Er³⁺. Population relaxation times (T₁) at about 850 ± 60 μs and 1010 ± 50 μs and dipole relaxation times (T₂) with values of 1100 ± 120 ns and 14.2 ± 0.3 ns have been obtained for the two components measured for the Yb³⁺:²F_7/2—²F_5/2 transition. T₁ = 402 ± 8 μs and T₂ = 11.9 ± 0.2 ns values have been found for the Er³⁺:⁴I_15/2—⁴I_11/2 excitation. The spectral diffusion rate at about 1 and 5 MHz/ms has been determined for the narrow and broad spectral line in Yb³⁺-doped crystal, respectively. The temperature dependence of the spectral hole halfwidth has also been investigated.