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.

In this work, the downconversion (DC) behaviour of Ho3+ ions doped in pure YVO 4 , YNbO 4 , YTaO 4 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 YVO 4 , YNbO 4 and YTaO 4 as well as their intermixed compositions have been studied. The DS green emission of Ho3+ ion in vanadate host (λ exc = 326 nm) is 5 times stronger than in niobate host (λ exc = 262 nm) due to efficient energy transfer between [VO 4 ]3- and Ho3+ ion. The downshifting (DS) emissions are also investigated on direct excitation of Ho3+ ion in YVO 4 , YNbO 4 and YTaO 4 hosts on excitation with 450/456 nm (5I 8 →5G 6 transition of Ho3+ ion) wavelength. It is found that the overall DS emission intensity is dominant in YNbO 4 :Ho3+ phosphor due to low phonon frequency and larger particle size of YNbO 4. The Ho3+ doped in mixed hosts viz. YTa 1-x V x O 4 , YTa 1-y Nb y O 4 , YNb 1-z V z O 4 (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 YTa 1-x V x O 4 :0.01Ho3+, YTa 1-y Nb y O 4 :0.01Ho3+, respectively. Further, we also investigated quantum cutting (QC) in YNb 1-z V z O 4 :5 mol% Yb3+ (where z = 0, 0.25, 0.50, 0.75, 1.0) phosphors on UV excitation (λ exc = 262 and 326 nm). The intensity of QC NIR emission is found to increase with the incorporation of 'V' in YNb 1-z V z O 4 phosphors. The strongest QC emission is observed in pure YVO 4 host as compared to pure YNbO 4 as well as other mixed matrices. The QC efficiency of NIR emission for YVO 4 :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. [ABSTRACT FROM AUTHOR]