Investigations of the luminescence properties of charge compensation on Bi3+ doped CaMoO4:Eu3+ phosphors

Abstract

When a metal ion is substituted for an element with a different valence in the matrix, charge compensation is needed. The charge compensation may cause to a vacancy (for example in this work; 3Ca2+ → 2Eu3+ + a calcium vacancy). Both of according to a charge compensation condition and without this condition, we have synthesized a series of CaMoO4:Eu3+ phosphors and Bi3+ co-doped in CaMoO4:Eu3+ phosphors. A series of CaMoO4:Eu3+ phosphors satisfied with charge compensation condition were synthesized using the solid state reaction method. Comparing to uncompensated Ca0.95MoO4:0.05Eu3+ phosphor, the crystallinity of compensated Ca0.925MoO4:0.05Eu3+ phosphor is improved, and the lattice constant is increased. Also, CT band of Eu3+ – O2- and Mo6+ – O2- shifted towards the lower energy region due to the enhanced covalent bond interaction between the Eu3+/Mo6+ and O2-ions. The main emission of Ca0.925Eu0.05MoO4 is 5D0 → 7F2 transition of Eu3+ at 617.5 nm, and emission intensity significantly increases about 3.7 times than that of uncompensated Ca0.95Eu0.05MoO4. A series of the Bi3+ co-doped in CaMoO4:Eu3+ phosphors were fabricated to find out charge compensation with optimized. When Bi3+ ions are introduced to the phosphors, the self-absorption of Bi3+ from ground state (1S0) to the excited state (3P1) in the wavelength range below 360 nm are observed. Besides, the oscillator strength of the electric dipole transitions from emitted Eu3+ in the sample including Bi3+ ions is increased about 2.6 – 4 times than that of un-doped Ca0.95MoO4:0.05Eu3+. This is due to energy transfer from Bi3+ to Eu3+ and distortion of crystal field. With the compensated Ca0.91MoO4:0.05Eu3+, 0.01Bi3+ phosphor, it occur the increasing intensity of excitation and emission compared with uncompensated Ca0.94MoO4:0.05Eu3+, 0.01Bi3+. The emission intensity is increased about 2.5 times than uncompensated Ca0.94MoO4:0.05Eu3+, 0.01Bi3+. The result indicates that appropriate dopant of Bi3+ ions is related with charge compensation. Of these materials, Ca0.91MoO4:0.05Eu3+, 0.01Bi3+ exhibits the strongest red emission. The integral emission intensity of Ca0.91MoO4:0.05Eu3+, 0.01Bi3+ phosphor under excitation wavelength of 397.5 nm is about 3.4 times higher than that of commercial Y2O3:Eu3+ phosphor.