Yb3+-mediated white upconversion and high-sensitivity thermometry of Er3+, Yb3+, Tm3+ doped YNbO4 phosphors under 808 nm excitation

Abstract

A series of YNbO₄:Er³⁺,Yb³⁺,Tm³⁺ is prepared by the solid-state reaction method. No significant structure changes are found in prepared samples by X-ray diffraction characterization. Blue, green and red emissions of ¹G₄→³H₆ for Tm³⁺, and ²H_11/2/⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 for Er³⁺ can be obtained in Er³⁺,Yb³⁺,Tm³⁺ co-doped system under 808 nm excitation, and the upconversion mechanism are investigated in detail. Complex energy transfer and cross relaxation make it difficult for Er³⁺,Tm³⁺ system to bring Tm³⁺ blue emission of ¹G₄→³H₆, whereas the Yb³⁺ mediated effect plays a key role in the population of blue emitting level for Tm³⁺. Moreover, YNbO₄:Er³⁺,Yb³⁺,Tm³⁺ can realize thermometry with high sensitivity performance of 7.7 × 10⁻³ K⁻¹ for S_A and 1.2 % K⁻¹ for S_R. The tri-doped system showing excellent color tunability can achieve multi-color upconversion luminescence including white light emission, which has the potential to be applied in solid-state displays, optical thermometry and light-emitting diodes.