Structure-Dopant Concentration Relations in Europium-Doped Yttrium Molybdate and Peak-Sharpening for Luminescence Temperature Sensing.

A set of Eu-doped molybdates, YxEuxMoO (x = 0.04; 0.16; 0.2; 0.4; 0.8; 1; 1.6; 2), was synthesized using a solid-state technique and their properties studied as a function of Eu concentration. X-ray diffraction showed that the replacement of Y with larger Eu resulted in a transformation from orthorhombic (low doping concentrations) through tetragonal (high doping concentrations), reaching monoclinic structure for full replacement in EuMoO. The intensity of typical Eu red emission slightly increases in the orthorhombic structure then rises significantly with dopant concentration and has the highest value for the tetragonal YMoO:80mol% Eu. Further, the complete substitution of Y with Eu in the case of monoclinic EuMoO leads to decreased emission intensity. Lifetime follows a similar trend; it is lower in the orthorhombic structure, reaching slightly higher values for the tetragonal structure and showing a strong decrease for monoclinic EuMoO. Temperature-sensing properties of the sample with the highest red Eu emission, YMoO:80mol% Eu, were analyzed by the luminescence intensity ratio method. For the first time, the peak-sharpening algorithm was employed to separate overlapping peaks in luminescence thermometry, in contrast to the peak deconvolution method. The Sr (relative sensitivity) value of 2.8 % K was obtained at room temperature.