The paper is focused on an influence of vanadium ions on the up-conversion processes in nanosized YV x P 1−x O 4 solid state solution. As a consequence, two series of YV x P 1−x O 4 (where x = 0–1) materials has been obtained via co-precipitation method. Yttrium orthovanadate-phosphate has been co-doped with the up-converting Er3+-Yb3+ and Tm3+-Yb3+ lanthanide ion pairs. Obtained series of nanosized materials has been investigated for phase purity, chemical composition, morphology by the means of X-Ray Powder Diffraction (XRD) and Scanning Electron Microscope (SEM). Photoluminescence properties of 0.25 mol% Tm3+, 20 mol% Yb3+:YV x P 1−x O 4 (x = 0, 0.3, 0.4, 0.5, 0.6, 0.7, 1), and 1 mol% Er3+, 20 mol% Yb3+:YV x P 1−x O 4 (x = 0, 0.3, 0.4, 0.5, 0.6, 0.7, 1) were investigated in detail. It has been found that increase of the vanadium content leading to better up-conversion luminescence. [Display omitted] • Co-precipitation synthesis method lead to obtaining pure YV x P 1-x O 4 co-doped with Tm3+–Yb3+ and Er3+–Yb3+ ions. • Structural and morphological analysis confirmed that materials were nanosized and in accordance with the Vegard's law. • Influence of changing V5+ ion concentration on up-conversion luminescence of Tm3+–Yb3+ and Er3+–Yb3+ was investigated. • Energy level scheme with proposed up-conversion processes (ETU, ESA, CS and CR) was presented. [ABSTRACT FROM AUTHOR]