A study of optical properties of Sm3+ -doped M′ -type structure YTaO4 powders synthesized by the disodium tetraborate flux method

The Y1-xSmxTaO4 (x = 0.1, 0.5, 1.0, 2.0 and 5.0) compounds have been synthesized by conventional solid state method using disodium tetraborate as flux. The growth process of title compounds was studied using X-ray diffraction and electron microscopy (SEM and TEM). The powder diffraction pattern was indexed on a monoclinic cell, space group P2/a, lattice parameters: a = 5.302, b = 5.454 and c = 5.115 Å, Z = 2 and V = 146.97 Å3. The absorption (300 K) and fluorescence spectra (5 and 300 K) as well as the fluorescence dynamics of the Sm3+:YTaO4 are presented and analysed in detail. The room-temperature absorption spectra have been analysed using the Judd-Ofelt approach. The intensity parameters have been evaluated and subsequently used to calculate fundamental spectroscopic parameters: the spontaneous transition probabilities, the branching ration, emission cross-sections and natural lifetime for the 4G(4)5/2 emitting level. The luminescence spectra recorded between 5 and 300 K are composed of transitions from the 4G(4)5/2 level to the 6H5/2, 6H7/2, 6H9/2, 6H11/2, 6H13/2, 6H15/26F1/2, 6F3/2 and 6F5/2 levels. The maximum emission cross-section has been calculated to be 0.935 and 0.985 × 10−21 cm2 at 609.1 and 657.1 nm, respectively. The electron-phonon coupling parameter α¯ was found to be in the range 127-512 cm−1 for the 4G(4)5/2 → 6H5/2, 4G(4)5/2 → 6H7/2 and 4G(4)5/2 → 6H9/2 transitions.