Real-time naked-eye recognizable temperature monitoring based on Ho ³⁺ (or Tm ³⁺ )-activated NaYF ₄ upconversion nanowires: via visual multicolor alteration

Non-contact thermometry for real-time temperature monitoring is a challenging research topic. Advances in microelectronics and biotechnology demand precise temperature monitoring with novel materials and approaches, where conventional thermometers are burdensome because of employing expensive additional equipment (e.g. spectrometers) and further data processing. Lanthanide-doped upconversion nanomaterials that can convert single near-infrared excitation into multicolor visible emissions open the door for a novel strategy to thermometry. Herein, a real-time naked-eye recognizable color change was achieved based on Ho ³⁺ (or Tm ³⁺ )-activated NaYF ₄ upconversion nanowires, depending on the different spectral sensitivities of the blue, green and red upconversion emissions to temperature. Furthermore, the luminescence color can be also directly modulated by only using 975 nm laser radiation, which extended their application scope. These desirable properties make upconversion nanomaterials promising for temperature monitoring, anti-counterfeiting, and multicolor temperature probing applications with the advantages of being simple, convenient and unreplicable.