Effect of ligand field symmetry on upconversion luminescence in heat‐treated LaBGeO5:Yb3+, Er3+ glass.

Abstract: In this paper, we report upconversion (UC) luminescence enhancement in LaBGeO₅:Yb³⁺, Er³⁺ glass‐ceramics (GCs), surface crystallized glass‐ceramics (SCGCs) and ceramics compared with the as‐melt glass fabricated by the conventional melt‐quenching technique. Based on structural investigations, we find that the nucleation and crystallization of trigonal stillwellite LaBGeO₅:Yb³⁺, Er³⁺ nanocrystals occur first at the glass surface before the following volume crystallization. The local site symmetry around rare earth (RE) ions which was evaluated using the Eu³⁺ ions as a probe together with Judd‐Ofelt theory calculations exhibits a clear increase with the devitrification of the glass. Consequently, complete crystallization of the glass leads to largest enhancement in the UC emissions of the LaBGeO₅:Yb³⁺, Er³⁺ ceramics. We ascribe the enhancement of UC luminescence in the LaBGeO₅:Yb³⁺, Er³⁺ GCs, SCGCs, and ceramics to the structural ordering and the improvement of site symmetry surrounding RE ions that minimizes the rate of nonradiative relaxation process. [ABSTRACT FROM AUTHOR]