The luminescence of (nano)materials is often sensitive to temperature. This enables thermometry experiments with micrometer resolution by simply inserting this type of thermometers in a relevant sample, followed by remote acquisition of the emission spectrum. The development of luminescent thermometers is mainly focused on the maximization of spectral changes for small temperature variations. However, it is still unclear how luminescent thermometers perform in the actual application. In this thesis, we have investigated the experimental errors of luminescent thermometers to better understand what affects the reliability of temperature measurements. Our work shows how errors due to noise, introduced by the photodetector, determine the uncertainty in the measured temperature. We further observed systematic errors in the measured temperature during our measurements with micrometer spatial resolution, which we attribute to the local photonic environment of the thermometer. In addition, we have examined methods to extend the temperature range of luminescent thermometers and developed new materials to achieve this. Our research shows that thermometer design is crucial for minimizing both measurement uncertainties and systematic errors. These insights can help to optimize new and existing thermometers, which is an important step for reliable application.