Enhancement of upconversion luminescence in Er3+ doped tellurite glasses due to the introduction of PbCl2

The upconversion properties of Er3+ doped lead chloride tellurite glasses under 980 nm excitation are investigated. Three intense emission bands centered at 525, 547, and 657 nm corresponding to the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2, respectively, simultaneously occurs. The important role of PbCl2 in upconversion intensity is observed and its influence on the green (547 nm) and red (657 nm) emissions is compared and discussed. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The high-populated 4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes.