Luminescence and energy transfer performances of Tb3+/Mn4+ co-doped Sr2LuTaO6 double-perovskite phosphors for a highly sensitive optical thermometer

Abstract

A series of Tb³⁺/Mn⁴⁺ co-doped double-perovskite oxides Sr₂LuTaO₆ (SLT) phosphors are synthesized by a solid-state method. The results of structural characterization prove that the Tb³⁺ and Mn⁴⁺ ions are successfully doped into the SLT host. The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Sr₂LuTaO₆:Tb³⁺, Sr₂LuTaO₆:Mn⁴⁺ and Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ are illustrated in detail. Under ultraviolet (UV) excitation, bright green and red lights are obtained from the Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ phosphor. In particular, the emission intensity of Tb³⁺ ions in Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ is enhanced by the energy transfer (ET) process from Mn⁴⁺ to Tb³⁺. The thermal enhancement of Tb³⁺ ion radiation in Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ also proves the ET process (Mn⁴⁺ → Tb³⁺). In addition, the thermal enhancement of Tb³⁺ ion radiation and the thermal quenching of Mn⁴⁺ ion radiation in the Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ system can be applied to develop optical thermometry based on luminescence intensity ratio (LIR) technology. Therefore, the LIRs of Mn⁴⁺ (²E_g → ⁴A_2g) and Tb³⁺ (⁵D₄ → ⁷F_5,4) are investigated in the temperature range from 313 to 573 K. The absolute sensitivity (S_a) and relative sensitivity (S_r) of the Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ phosphor are calculated. The maximum values of S_a and S_r are obtained from the LIR of Tb³⁺: ⁵D₄ → ⁷F₄ (570–599 nm) and Mn⁴⁺: ²E_g → ⁴A_2g (625–705 nm). The maximum S_a is 10.18% K⁻¹ at 543 K, and the maximum value of S_r reaches 1.98% K⁻¹ at 543 K. These results confirm that the ET process from Mn⁴⁺ to Tb³⁺ contributes to increasing the temperature measuring sensitivity of the Sr₂LuTaO₆:Tb³⁺/Mn⁴⁺ phosphor. Therefore, the Sr₂LuTaO₆:Mn⁴⁺/Tb³⁺ phosphor has prospective potential in optical thermometry and provides advantageous guidance for designing high-sensitivity optical thermometers.