We evaluate the sensitivity and thermal resolution of the fluorescence of europium (III) thenoyltrifluoroacetonate (EuTTA) in order to convert absorbed thermal radiation into visible. We analyze the variation of the fluorescence properties of EuTTA (specifically, amplitude power and lifetime) after absorbed thermal radiation has caused a change in the local temperature of the material. We propose to analyze the thermal dependence of the fluorescence decay with an integral functional. Such operation correlates the variations of lifetime and amplitude in a single value. With this method of analysis, we study one param eter with increased thermal resolution and linear temperature dependence. The thermal resolution achieved with amplitude power is $0.11\mathrm{K}$ and with lifetime is $0.83\mathrm{K}$ at $305\mathrm{K}$ . The sensitivity of the integral functional is $25\mathrm{nJ}/\mathrm{K}$ , yielding an increased thermal resolution of $0.07\mathrm{K}$ .