Photoluminescence of CaxBa1−xGa2S4:Eu2+ solid solutions in wide excitation intensity and temperature intervals

The detailed investigation of CaxBa1−xGa2S4:Eu2+ solid solutions photoluminescence caused by 5d→4f electronic transitions in Eu2+ ions with x value from 0.1 to 0.9 in wide excitation intensity and temperature intervals was performed. It is shown that the change of x from 0.1 to 0.9 appears in a tune of emission spectrum peak position from 506 nm to 555 nm with minimal losses in the integral intensity not more than by 8%. The long wavelength shift of the emission spectra was determined as a result of the rise in the crystal field splitting energy of 5d-orbitals of Eu2+ ions in thiogallate host with increasing Ca content, which decreases the energy of the 5d→4f emission transition. The energies of the zero phonon line, red shift and the Stokes shift were defined for x value from 0.1 to 0.9. High temperature stability of the integral emission intensity with a decrease at only 25-40% depending on x value was found in the range from 10 K to 400 K. It was revealed that the increase in Ca content leads to a reduction of the temperature shift of the emission spectrum whereas at x≥0.5 the shift is absent. The photoluminescence decay time constants were found to be from 305 ns to 470 ns for x value from 0.1 to 0.9. The extreme stability of the emission band shape and spectral position was found in a wide range of excitation power density from 10−3 W/cm2 to 107 W/cm2 with a reversable emission efficiency droop only above 2·104 W/cm2.