Growth, vibrational and luminescence analysis of monoclinic KGd(1−x)Prx(WO4)2 (x=0.005, 0.02, 0.05) single crystals

Growth of pure KGW, 0.5, 2 and 5 wt% Pr3+ doped KGd(WO4)2 single crystals were carried out using top seeded solution growth (TSSG) method with K2WO4 as flux. Growth parameters that include the cooling rate and pulling rate were modified to achieve transparent doped crystals to that of pure crystals. Optically polished samples were used for optical and structural studies. Structure of grown crystals was confirmed and lattice parameter values were calculated using single crystal X-ray diffractometer. Both pure and doped crystals belong to the monoclinic phase with C2/c space group. When compared to pure matrix of KGW, some notable changes were observed in the lattice parameter values of doped crystals. It may be due to the ionic radii mismatch of replacing praseodymium ion in the place of gadolinium ion. Absorption and emission measurements were carried out for the 2 mm thick polished samples. The doped samples show a very good transparency with an intense absorption band around the blue region of the spectrum with additional absorption peaks in the IR region as well. Strong red emission was observed in the emission spectrum. The energy levels and their corresponding transitions were figured out in Pr3+ ions inside the matrix. Emission characteristics were compared for different dopant concentration. Raman spectra reveal the intense tungstate vibrational modes in the higher frequency region. Comparison of pure and doped samples reveal that there is no significant change in vibrational modes at higher doping concentration.

► Growth of 0.5, 2 and 5 wt% Pr3+:KGW crystals was carried out with low viscous flux.
► Single crystal XRD results reveal the influence of Pr3+ ion in the KGW matrix.
► Emission results confirm the 1D2→3H4 (red) and 3P0→3H4 (Greenish Blue) transitions.
► There was concentration depended quenching of de-excitation transition of 1D2.
► Raman spectra reveal the formation of double bridge tungsten oxide chains.