Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Gd, Y) Borate Single Crystals

Abstract

Synthesized powders and grown single crystals of nominal compositions Li(6)Ln(BO(3))(3):Yb(3+) (Ln=Y, Gd) were investigated by means of powder and single-crystal X-ray diffraction (XRD), as well as optical near-IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero-phonon lines suggests the existence of two kinds of Yb(3+) ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y(3+). A strong temperature dependence of the intensity of Yb-Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb(3+) is in good agreement with crystallographic ones: R=3.856 Å, R(cryst) =3.849 Å.

Closely-Related ZnII2LnIII2 Complexes (LnIII = Gd, Yb) with Either Magnetic Refrigerant or Luminescent Single-Molecule Magnet Properties

“…It is possible that two different assignments of the above transitions could be made: (a) the observed bands may correspond to the four components expected from the 2 F 5/2 → 2 F 7/2 transition arising from the ligand field splitting of the 2 F 7/2 multiplet. Although the position of the emission bands and consequently the energy gap between the ground and first excited state ∼315 cm –1 and the total splitting ∼665 cm –1 are similar to those found for the ytterbium-doped Li 6 Y(BO 3 ) 3 compound (where the Yb III ion also exhibits a YbO 8 coordination environment), these values are larger than those usually calculated and observed for other YbO 8 complexes . In addition to this, an argument against this assignment is that the energy gap between the ground and first excited state would be exceedingly larger than the energy gap calculated from the simulation of the dc susceptibility data with the above crystal-field Hamiltonian.…”

“…(The other three bands appear at almost the same energies as in the emission spectrum of 2 .) Although its origin is unclear, the apparent weak band at the lowest energy (1045 nm) could be tentatively attributed to, among other things, the crystal growth process leading to the creation of different Yb III defects in the polycrystalline sample, or to a strong interaction of the Yb III ion with lattice vibrations, which would result in additional vibronic transitions in the spectra, or to local Yb III –Yb III interactions inducing modifications in the crystal-field splitting of the 2 F 7/2 ground multiplet . In view these considerations it is reasonable to assume that the second assignment (b) is more probable.…”

Optical and EPR spectroscopy of Er3+ in lithium yttrium borate, Li6Y(BO3)3:Er single crystals

“…For most applications the crucial point is the accurate determination of the energy levels of the RE ions in the matrix. The LYB:Yb 3+ system has been well documented by Sablayrolles et al [3,5,9], Jubera et al [10], and Brenier et al [11]. Although some spectroscopic properties of Er 3+ in LYB measured at room temperature have also been reported [12,13], a detailed spectroscopic analysis of the LYB:Er 3+ system is still missing.…”

“…The site occupation of Er 3+ and the possible RE pair formation found e.g. in Yb 3+ doped LYB, which may induce modifications in the Stark component splitting [10], will also be discussed for Er 3+ doped LYB single crystals.…”