Red-emitting CaWO4:Eu3+,Tm3+ phosphor for solid-state lighting:Luminescent properties and morphology evolution

CaWO4:xEu3+,yTm3+crystals were obtained by facile synthesis at low temperature by the microwaveassisted hydrothermal method(MAH).The phase formation,morphology,luminescent properties and ene rgy transfer were investigated.The X-ray diffraction(XRD) re sults show the formation of a scheelitelike tetragonal structure without the presence of secondary phases.The growth mechanism of hierarchical micro structures based on self-assembly and Ostwald-ripening processes was evaluated,obtaining different types of morphologies.The luminescence spectra of CaWO4:Eu3+,Tm3+at 325 nm excitation show the predominance of red emission at the ~5 D0→~7 F2(Eu3+) transition at 624 nm.This feature signals dominant behavior of the electric dipole type.The presence of Tm3+is notably evident in the absorption spectra by the related excitation transitions:~3 H6→~1 G4,~3 H6→~3 F3and ~3 H6→~3 H4.Color parameters are discussed to characterize CaWO4:Eu3+,Tm3+emission.The study of the emission spectrum as a function of the concentration of Eu3+(x mol%) and Tm3+(y mol%) indicates that the CaWO4:Eu3+,Tm3+phosphors show stronger red emission intensity and exhibit the CIE value of x=0.63 and y=0.35.The photoluminescence results show 97% high color purity for CaWO4:4 mol%Eu3+,a high CRI(92%) and a low CCT of 1085 K.These results demonstrate that the CaWO4:Eu3+,Tm3+red phosphors are promising as color converters for application in white light-emitting diodes and display devices.