Fluorescence in flux-grown single crystals of lithium praseodymium tetraphosphate (LiPrP4O12) and lithium thulium tetraphosphate (LiTmP4O12) has been studied under UV excitations with LEDs at six wavelengths between 245 nm and 315 nm. The emissions observed at room temperature have been assigned by means of known energy-level differences from absorptions of the same single crystals. Many more 4f-4f emissions have been found under the mentioned UV excitations compared to earlier studies with excitation wavelengths higher than 450 nm. The fluorescence measurements have been used to construct the 4f energy-levels diagrams of Pr3+ and Tm3+ ions in these compounds. (C) 2017 Elsevier GmbH. All rights reserved.