Broad-Scope Thermometry Based on Dual-Color Modulation up-Conversion Phosphor Ba₅Gd₈Zn₄O₂₁:Er³⁺/Yb³⁺

Abstract

Yb3+/Er3+ codoped Ba5Gd8Zn4O21 up-conversion (UC) phosphors with tunable emission were synthesized using a facile sol–gel method. UC spectra are composed of green emission from 2H11/2/4S3/2 → 4I15/2 transitions and red emission from 4F9/2 → 4I15/2 transition of Er3+ ion with the excitation of 980 nm laser diodes. Modulation of emitting color from green to red could be achieved by adjusting dopant concentrations or pulse width of 980 nm laser. The mechanism of the former strategy was figured out through analyzing visible and near-infrared (NIR) down-conversion emission spectra together with the corresponding green level (4S3/2) lifetimes under excitation of 490 nm light, and the latter method was explained by the non-steady-state up-converison process. Temperature detection range was expanded to low temperature region by utilizing red-emitting stark levels of Er3+ ion as thermally coupled levels. Thermal sensing performances based on green-emitting levels (2H11/2/4S3/2) and red emitting stark levels (4F9/2(1)/ 4F9/2(2)) of Er3+ ion were estimated and the maximum sensitivity are 0.0032 K–1 at 490 and 0.0029 K–1 at 200 K in our experimental range, respectively. Moreover, the effects of UC emission color from different dopant concentrations and pulse widths of lasers on sensor sensitivity were also investigated in detail. Results imply that the present phosphor Ba5Gd8Zn4O21:Er3+/Yb3+ exhibits high and stable sensitivity in a wide temperature detection scope, which makes it an excellent candidate for an optical thermometer.

Physical Background for Luminescence Thermometry Sensors Based on Pr3+:LaF3 Crystalline Particles

“…Therefore, the local temperature inside bulk crystal can be estimated by (1). The absolute and relative sensitivities ( and ) can be expressed by the following equations [6,33,34]:…”

Highly efficient upconversion of Er3+ in Yb3+ codoped non-cytotoxic strontium lanthanum aluminate phosphor for low temperature sensors

“…Moreover, the UC intensity of SLA:Er is too low to be used practically in comparision to the SLA:Er/Yb samples. From literature it is also evident that the sensitivity of SLA:Er and SLA:Er/Yb phosphors are also in accordance to the low phonon hosts such as fluorides, rare earth oxides etc that are highly used in bio-imaging due to their high UC efficiencies in spite of their toxic nature 1,50–54 .…”

“…1–5 . Fluorescence intensity ratio (FIR) technique is widely used for the temperature sensors based on glasses/glass-ceramics doped with RE 3+ , providing high detection spatial resolution, precision and excellent sensitivity 5–7 .…”

Improving Optical Temperature Sensing Performance of Er3+ Doped Y2O3 Microtubes via Co-doping and Controlling Excitation Power

“…The thermal coupled levels of 4 F 9/2(1) and 4 F 9/2(2) are populated by the NR process from the 4 S 3/2 level. According to the Boltzmann distribution 14, 15 , the population of the 2 H 11/2 level increases with respect to the 4 S 3/2 with the increase of the temperature, owe to the low energy difference between 4 S 3/2 and 2 H 11/2 levels. The thermalization of the 2 H 11/2 level is dominant and the depopulation induced by the NR process can be neglected.…”