A.A. Lyapin, S.V. Kuznetsov, P.A. Ryabochkina, A.P. Merkulov, M.V. Chernov, Y.A. Ermakova, A.A. Luginina, P.P. Fedorov. Upconversion luminescence of Ca_1-xHo_xF_2+x and Sr_0.98-xEr_0.02Ho_xF_2.02+x powders under excitation by infrared laser // Laser Phys. Lett. 14 (2017) 076003. https://doi.org/10.1088/1612-202X/aa7418