Er 3+ /Yb 3+ /Ho 3+ tri-doped no-core fiber temperature sensor based on fluorescence intensity ratio technology: towards high stability and accurate measurements.

In this paper, the green upconversion (UC) fluorescence emission from E r ³⁺ / Y b ³⁺ / H o ³⁺ tri-doped tellurite glass is investigated for temperature sensing. The doping of H o ³⁺ ions not only enhances the chance of energy level transition but also avoids the influence of the thermal effect caused by the proximity of ² H _11/2 and ⁴ S _3/2 energy levels. The luminescence characteristics at different Y b ³⁺ and H o ³⁺ ion concentration doping molar ratios were investigated, and the strongest luminescence characteristics were exhibited when the Y b ³⁺ ion concentration was at 5 mol% and H o ³⁺ at 0.2 mol%. Based on this, a tri-doped T e O ₂ - Z n O - B i ₂ O ₃ (TZB) no-core fiber was fabricated and connected with multimode fibers (MMFs) to form a temperature sensor. The temperature sensing performance of the tri-doped TZB temperature sensor was evaluated in detail over the temperature range of 255-365 K. The repeatability and stability of the temperature sensor was experimentally verified. The E r ³⁺ / Y b ³⁺ / H o ³⁺ tri-doped sensor can be used for noninvasive optical temperature sensing in the fields of environmental monitoring, biological sensing, and industrial process temperature control, etc.