Spectroscopic and structural characterization of transparent fluorogermanate glass ceramics with LaF3:Tm3+ nanocrystals for optical amplifications

Abstract

Transparent Tm3+-activated glass ceramics (GC) with ∼26% LaF3 nanocrystallites were developed from the 50GeO2–22Al2O3201313LaF3–15LiF (mol%) glass system. Upon excitation at 468 and 688nm, GC with 0.3mol% Tm3+-doping (GC0.3Tm) reveals remarkably enhanced luminescence within 600–850nm range. This could be ascribed to the change in ligand environment around Tm3+ as evidenced by the decrease of Ω2 from 4.32 (PG0.3Tm) to 3.79 (GC0.3Tm) after ceramming. The concurrent intense infrared emission at ∼1.2 and 1.46μm exhibits a respective full width at half maximum of 76 and 106nm, mean decay time of 229 and 467μs. The stimulated emission cross sections and gain parameters were evaluated using radiative parameters derived from Judd–Ofelt (J–O) analysis. Further discussions on the local structure around rare earth ions are based on Eu3+ as a probe. For GC with 0.05mol% Eu3+-doping (GC0.05Eu), the obvious stark splitting and significantly (6-fold) enhanced emission originating from the excited Eu3+:5D3→1 states is consistent with the red shift of diffraction peaks, revealing the partition of Eu3+ into LaF3 nanocrystals.