Photoluminescence and ratiometric optical thermometry in Mn4+/Eu3+ dual-doped phosphor via site-favorable occupation

Abstract

Optical temperature sensing has been concerned owing to its unique advantages. At present, most researchers construct optical thermometers using optical materials based on thermally coupled levels (TCLs) of rare earth ions. However, it cannot satisfy high temperature sensitivity and good signal discriminability at the same time. Hence, a new temperature sensing strategy based on dual activators is proposed in order to solve the above questions. One of the biggest challenges of this strategy currently faced is the two activators sometimes cannot be excited simultaneously and emit light. Herein, we have designed Mn4+/Eu3+ co-doped double-perovskite type NaLaMgWO6 (NLMW) phosphors via site-favorable occupation principle and investigated their applications in optical temperature sensing. The study showed that Mn4+ and Eu3+ will prefer occupy different cation sites when they enter to the host. Investigating the temperature-dependent luminescence properties of NLMW:Mu4+,Eu3+ phosphor in the range of 303 K–523 K found that both Eu3+ and Mn4+ can emit red emissions but the fluorescence intensity of Mn4+ is much higher than that of Eu3+. And due to Mn4+ and Eu3+ ions have different thermal response where the luminescence intensity of Mn4+ ion decreased more quickly than that of Eu3+ as the temperature increasing, the Mn4+ ion is suitable as temperature signal and Eu3+ ion can be used as reference signal and the fluorescence intensity ratios (FIR) of Mn4+ to Eu3+ were significantly influenced by temperature. Meanwhile, we calculated the thermal quench activation energy of Eu3+ and Mn4+ according to the relationship between intensity and temperature, which are 1.83 eV and 0.367 eV, respectively. Based on the FIR, we further analysed the temperature sensitivity and found that the maximum relative and absolute sensitivity were as high as 0.86% K−1 (523 K) and 3.02% K−1 (363 K), respectively, which is higher than most optical materials based on TCLs. All results indicate that the obtained phosphor could be used to construct self-referencing optical thermometry based on double luminescent centers.