Optical Vacuum Sensor Based on Lanthanide Upconversion—Luminescence Thermometry as a Tool for Ultralow Pressure Sensing

Abstract Currently the lowest optically determinable pressure values are around 10² bar, making the pressure below inaccessible for optical detection. This work shows for the first time how to overcome these limitations, and optically monitor the low pressure values in a vacuum region (from ≈10⁻⁵ to 10⁻² bar), utilizing the light‐induced and pressure‐governed heating–cooling of the material. Herein, the well‐defined temperature dependency of the luminescence intensity ratio of the Er³⁺ thermally‐coupled levels (TCLs), is used to monitor the elevation of local temperature of the upconverting material (YVO₄:Yb³⁺‐Er³⁺), induced by a NIR laser irradiation. The unprecedented enhancement (≈20 times) of the laser‐induced heating of the sample observed under vacuum conditions, is used to convert the luminescent thermometer into the remote vacuum sensor. The variations of pressure in the system are correlated with changes of the band intensity ratio (525/550 nm) of Er³⁺ TCLs, which are further applied for the remote, contactless vacuum sensing.