Effects of Yb3+ ion doping on lattice distortion, optical absorption and light upconversion in Er3+/Yb3+ co-doped SrMoO4 ceramics

Abstract

Sintered ceramic pellets of rare-earth ion doped strontium molybdate compositions Sr1-x-yErxYbyMoO4 (x = 1 mol%; y = 0–9 mol%) were prepared using solid-state reaction method. Rietveld refinement of HR-XRD data reveals a high degree of lattice distortion for y = 3 mol %, and correspondingly a maximum deviation in the O–Sr–O and Mo–O bonds. Raman spectroscopy indicates the substitution of Er3+ and Yb3+ at the SrO8 polyhedron clusters of the SrMoO4 unit cell, and infrared absorption shows changes in the molybdenum-oxygen (Mo–O) bond strength in the [MoO4]2⎻ cluster. Variations in the optical band gap are attributed to positional change of oxygen octahedra and local bond distortion in the unit cell. A selective enhancement in green up-conversion luminescence is seen at y = 3 mol %, and originates due to direct contribution from the [Yb3+⎼MoO4]2- dimer complex sensitization, and correlates with the presence of high lattice distortion. A progressive increase in lifetime of the 4S3/2 from 0.195 to 0.424 ms at y = 0.03 increase the radiative transition probability and UC emission. Luminescence quenching for Yb3+ ion content (y > 0.03) is due to the reduced asymmetrical arrangement around erbium ion and corresponding changes in the Sr–O and Mo–O bond lengths. These studies provide new insight into the quenching effect and formulate a new strategy to design ceramic compositions for better UC performance.