**Abstract**

Luminescent lanthanide complexes serve as a unique set of tools for creating sensory materials. The most significant types of sensory response in such materials are the turn-on/off response, when the analyte causes an increase or decrease in the emission intensity, respectively, as well as the ratiometric response, which manifests itself as a change in the ratio of luminescence intensities at different wavelengths. In this paper, we consider two of the most technologically advanced types of luminescent sensor materials based on lanthanide compounds—"turn on" and ratiometric sensors. The production of such materials is not only of importance per their possible application but is especially interesting from a fundamental point of view, since their design requires the implementation of non-trivial solutions.

**Keywords:** lanthanides, coordination compounds, luminescence, sensors, sensory response mechanism, turn-on sensors, ratiometric sensors
