Upconversion luminescence and temperature sensing characteristics of Ho³⁺/Yb³⁺ co-doped tellurite glasses

The upconversion emission spectra of Yb³⁺/Ho³⁺co-doped TeO₂-ZnO-BaO glasses were studied for solid-state lighting and optical thermometry. The studied glasses were prepared using the melt quenching technique. The green and red UC emissions of Ho³⁺ions are due to two-photon absorptions, which cause the various energy transfer processes. The studied glasses show tunable color properties and high-temperature sensor sensitivity. Color coordinates on the CIE chromaticity diagram of those were affected by the pump power and shifted from green to red region at higher Ho³⁺concentrations. The ⁵F₅ level and (³F₄,⁵S₂) levels of Ho³⁺ are found to be thermally coupled levels. The energy difference (ΔE) between these levels is calculated as 2463.66 cm⁻¹. Among the studied glasses, Yb³⁺(3.0 mol%)/Ho³⁺(0.15 mol %) co-doped TeO₂-ZnO-BaO show the highest absolute sensitivity of 0.011K⁻¹ at 503K. In the light of conducted observations, the studied glasses are proposed as a good candidate material for lighting and optical temperature sensing.