Comparative study of structural, optical and magnetic properties of Er3+ doped yttrium gallium borates

Abstract

The paper presents the results of a comprehensive study of yttrium gallium borate (YGa3(BO3)4) crystals low-doped (0.2 wt%) with erbium (Er3+) ions by in-situ X-ray diffraction (XRD), radioluminescence (RL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. Structural and elastic properties of YGa3(BO3)4: Er3+ crystals measured by the XRD method in the temperature range from 300 K to 1073 K have revealed the temperature variation of the volume thermal expansion coefficient. The analysis of RL spectra allowed us to assume the existence of the characteristic Er3+-related emission band located in the near-infrared region. The TSL spectra revealed strong peaks at low temperatures due to shallow traps and much less intense bands located above room temperature. Measurements of heat capacity in a wide temperature range allowed us to determine the Debye temperature θD ≈ 332 K. From the detailed analysis of the strongly anisotropic EPR spectra measured in YGa3(BO3)4:Er3+ crystals, the parameters of the spin Hamiltonian of Er3+ ions were determined: g⊥ = 9.34; g∥ = 1.269; A⊥ = 320.9 MHz; A∥ = 47.7 MHz. The temperature dependence of the spin-lattice relaxation rate of Er3+ ions was described well by the Orbach-Aminov process. It was proposed that Er3+ ions reside yttrium ions in YGa3(BO3)4 crystal lattice and are located in a slightly distorted prism made of six oxygen ions.