Ratiometric luminescence thermometry with trivalent lanthanide ions and their 4fⁿ energy levels is an emerging technique for non-invasive remote temperature sensing with high spatial and temporal resolution. Conventional ratiometric luminescence thermometry often relies on thermal coupling between two closely lying energy levels governed by Boltzmann’s law. Despite its simplicity, Boltzmann thermometry with two excited levels allows precise temperature sensing, but only within a limited temperature range. While low temperatures slow down the nonradiative transitions required to generate a measurable population in the higher excitation level, temperatures that are too high favour equalized populations of the two excited levels, at the expense of low relative thermal sensitivity. In this work, we extend the concept of Boltzmann thermometry to more than two excited levels and provide quantitative guidelines that link the choice of energy gaps between multiple excited states to the performance in different temperature windows. By this approach, it is possible to retain the high relative sensitivity and precision of the temperature measurement over a wide temperature range within the same system. We demonstrate this concept using YAl₃(BO₃)₄ (YAB):Pr³⁺, Gd³⁺ with an excited ⁶P_J crystal field and spin-orbit split levels of Gd³⁺ in the UV range to avoid a thermal black body background even at the highest temperatures. This phosphor is easily excitable with inexpensive and powerful blue LEDs at 450 nm. Zero-background luminescence thermometry is realized by using blue-to-UV energy transfer upconversion with the Pr³⁺−Gd³⁺ couple upon excitation in the visible range. This method allows us to cover a temperature window between 30 and 800 K.

使用三价镧系元素离子及其 4f ⁿ能级的比率发光测温是一种新兴的非侵入式远程温度传感技术，具有高空间和时间分辨率。传统的比率发光测温法通常依赖于玻尔兹曼定律控制的两个紧密结合的能级之间的热耦合。尽管很简单，但具有两个激发能级的玻尔兹曼测温法可以实现精确的温度传感，但只能在有限的温度范围内进行。虽然低温减缓了在较高激发能级中产生可测量布居所需的非辐射跃迁，但温度太高有利于两个激发能级的均衡布居，但代价是相对热灵敏度较低。在这项工作中，我们将玻尔兹曼测温的概念扩展到两个以上的激发能级，并提供定量指南，将多个激发态之间的能隙选择与不同温度窗口的性能联系起来。通过这种方法，可以在同一系统内的较宽温度范围内保持温度测量的高相对灵敏度和精度。我们使用 YAl ₃ (BO ₃ ) ₄ (YAB):Pr ³⁺ , Gd ³⁺以及激发的⁶ P _J晶体场和紫外范围内的 Gd ³⁺自旋轨道分裂能级来演示这一概念，以避免热黑即使在最高温度下的身体背景。这种荧光粉很容易被廉价且强大的 450 nm 蓝色 LED 激发。 零背景发光测温是通过在可见光范围内激发时使用 Pr ³⁺ -Gd ³⁺电偶的蓝光到紫外能量转移上转换来实现的。这种方法使我们能够覆盖 30 到 800 K 之间的温度窗口。