Ho3+ ion in a (Ba, La)-tellurite glass: Strong ∼2.0 μm NIR emission and Yb3+ aided efficient NIR to vis upconversion

• Upconversion, NIR luminescence properties of Ho in an Yb-codoped tellurite glass are studied.
• Both NIR and upconversion luminescence of Ho3+ are greatly enhanced in this glass.
• The results indicate strong electrostatic interactions of Ho3+ with the host’s nonbridging oxygen.
• The material is prospective for use both as eye-safe NIR laser medium and NIR sensor.

(Ba, La)-tellurite glasses doped respectively with only Yb3+, only Ho3+ and co-doped with (Yb3+ + Ho3+) have been prepared and their optical properties are studied. The experimental absorption and the emission spectra of the Ho3+ doped glass and calculations of its various Judd–Ofelt parameters, show that the Ho3+ ion in the glass has superior absorption and emission transition probabilities and higher emission rates and emission cross-sections. Similar spectroscopic studies on the Yb3+/Ho3+ co-doped – glass; on the other hand, demonstrate that the ∼2.0 μm emission of Ho3+ of the glass can further be enhanced by phonon assisted non-resonance energy transfer from Yb3+. The derived emission cross-section spectrum of the 5I7 → 5I8 transition of Ho3+ of the glass and its related gain spectrum, indicate that the glass is prospective for use as a tunable solid state laser medium in this spectral region 1.972–2.053 μm. Yb3+ → Ho3+ energy transfer phenomenon also helps the Ho3+ ions of the co-doped glass to exhibit strong green (545 nm) and red (600 nm) upconversion emission upon excitation of its Yb3+ ions by 980 nm laser. All the observed superior optical properties of Ho3+ ion in the glass have been explained in the light of crystal field effect of the host.