Study on Raman processes in spin-lattice relaxation of Yb3+ and Nd3+ in Ca5(PO4)3F monocrystals

Raman relaxation processes have been studied in a wide temperature range. Presented are the results of measuring the time of the spin-lattice relaxation T1 of Yb3+ ions in Ca5(PO4)3F single crystals in the temperature range of 1.5-115 K and of Nd3+ ions in Ca5(PO4)3F in the range of 50-115 K. Measurements of T1 of Yb3+ ion at low temperatures are carried out by the method of the EPR-signal pulse saturation, and the spin-phonon broadening of EPR lines is used for the range of 77-115 K and for Nb3+ ion. One-phonon (direct) processes predominate in the range of T < 5 K, and at T > 5 K the two-phonon (Raman) processes do. An expression has been derived describing the temperature dependence of the Raman processes. The Debye temperatures obtained from the spin-lattice relaxation of Nd3+ and Yb3+ in Ca5(PO4)3F single crystal strongly differ one from another and from the Debye temperature of the crystal itself