The impact of pure and mixed self-activated YXO4 phosphor materials (X=V, Nb and Ta) on downshifting and quantum cutting emission behaviours of Ln3+ doped (Ln3+=Ho3+ and Yb3+) ions

Abstract

In this work, the downconversion (DC) behaviour of Ho3+ ions doped in pure YVO4, YNbO4, YTaO4 hosts and their intermixed (i.e. Ta/V, Ta/Nb and Nb/V) compositions have been investigated and compared. The samples were synthesized by solid-state reaction technique at 1473 K. The UV–Vis absorption and photoluminescence behaviour of 1 mol % Ho3+ doped YVO4, YNbO4 and YTaO4 as well as their intermixed compositions have been studied. The DS green emission of Ho3+ ion in vanadate host (λexc = 326 nm) is 5 times stronger than in niobate host (λexc = 262 nm) due to efficient energy transfer between [VO4]3- and Ho3+ ion. The downshifting (DS) emissions are also investigated on direct excitation of Ho3+ ion in YVO4, YNbO4 and YTaO4 hosts on excitation with 450/456 nm (5I8→5G6 transition of Ho3+ ion) wavelength. It is found that the overall DS emission intensity is dominant in YNbO4:Ho3+ phosphor due to low phonon frequency and larger particle size of YNbO4. The Ho3+ doped in mixed hosts viz. YTa1-xVxO4, YTa1-yNbyO4, YNb1-zVzO4 (where x, y and z = 0, 0.25, 0.50, 0.75 and 1.0) phosphors also emit intense green DS emission along with their violet-blue band emission on ultraviolet (UV) excitation. The mixing of Ta/V and Ta/Nb enhances the blue emission of host matrix on UV excitation. The green emission is found to increase with ‘V’ and ‘Nb’ concentrations in YTa1-xVxO4:0.01Ho3+, YTa1-yNbyO4:0.01Ho3+, respectively. Further, we also investigated quantum cutting (QC) in YNb1-zVzO4:5 mol% Yb3+ (where z = 0, 0.25, 0.50, 0.75, 1.0) phosphors on UV excitation (λexc = 262 and 326 nm). The intensity of QC NIR emission is found to increase with the incorporation of ‘V’ in YNb1-zVzO4 phosphors. The strongest QC emission is observed in pure YVO4 host as compared to pure YNbO4 as well as other mixed matrices. The QC efficiency of NIR emission for YVO4:5 Yb has been calculated and found to 129%. Therefore, the prepared phosphor material is highly applicable to increase the efficiency of Si- solar cell by QC NIR emission.