Spectroscopic properties and photoluminescence of the Li2B4O7:Mn,Sm glass

Abstract

The Li2B4O7:Mn,Sm glass containing 1.0 mol.% MnO2 and Sm2O3 were researched by X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and optical spectroscopy methods. The studied glass of high optical quality was obtained by high temperature melting technique. Parameters of the local structure (interatomic distances and coordination numbers) of Li2B4O7:Mn,Sm glass were derived from XRD data analysis. The EPR and optical spectroscopy (absorption, luminescence excitation, emission, decay kinetics) show the presence of Mn2+(3d5) and Mn3+(3d4) impurity ions in the Li2B4O7:Mn,Sm glass. By EPR spectroscopy in the studied glass were identified three types of Mn2+ centres: single Mn2+ (1) centres in the strongly distorted sites (ratio of rhombic and axial constants, |E/D| ≤ 1/3), single Mn2+ (2) centres in the sites with almost cubic symmetry (D ≅ 0, E ≅ 0) as well as Mn2+ pairs and small clusters coupled by magnetic dipolar and exchange interaction, respectively. The Mn2+ EPR spectra parameters in the Li2B4O7:Mn,Sm glass have been determined at T = 295 K. Optical absorption spectrum of the Li2B4O7:Mn,Sm glass contains a very broad intense band peaked at 467 nm belonging to the 5Eg(D) → 5T2g(D) transition of Mn3+ ions and several weak narrow lines corresponding to the 6H5/2 → 6P3/2, 6H5/2 → 6F9/2, 6F7/2, 6F5/2 transitions of Sm3+ (4f5, 6H5/2) ions. Emission spectrum of the Li2B4O7:Mn,Sm glass exhibits a broad band corresponding to the 4T1g(G) → 6A1g(S) transition of Mn2+ ions and three characteristic bands in the yellow-orange-red range belonging to the 4G5/2 → 6H5/2, 6H7/2, 6H9/2 transitions of Sm3+ ions. Photoluminescence spectra (excitation and emission) and decay kinetics of the Mn2+ and Sm3+ ions in the Li2B4O7:Mn,Sm glass are interpreted in comparison with corresponding results for Li2B4O7:Mn and Li2B4O7:Sm glasses. Energy transfer processes Sm3+→Mn2+, Mn3+, and Mn2+→Mn3+ in the studied glass are considered.