Luminescence of rare earth vanadate associates in sulfates

Abstract

In some divalent metal sulfates (CaSO 4, PbSO4) the introduction of trivalent rare earth ions on the metal sites and pentavalent vanadium on the sulfur sites results in the formation of associates V0~-RE 3~. Energy transfer from the vanadate group to trivalent rare earth ions can be studied in these systems. It is shown that the transfer rate is temperature independent, but depends strongly on the choice of the host. In CaSO 4 the transfer rate in the associate is estimated to be~,108 s~',and in PbSO4~s 1. The low transfer rate in PbSO 4: RE,V is ascribed to the influence of the Pb 2~ions on the charge distribution in the vanadate group.

Energy-Efficient, High-Color-Rendering LED Lamps Using Oxyfluoride and Fluoride Phosphors

“…Also, there does not appear to be a relationship between the position of the Ce 3+ 5d 1 level and/or apparent Stokes shift (Figure ) with the thermal quenching (Figure ), an indication that nonradiative level crossing is not the key quenching mechanism in these phosphors. An additional factor that can increase barriers for Ce 3+ 5d 1 thermal ionization in these compositions is an effective positive charge on Ce 3+ when it replaces Sr 2+ /Ca 2+ . However, if improvements in thermal quenching were mainly due to an effective positive charge on Ce 3+ , there should be only small differences between O 2− -rich and F − -rich compositions, in contrast to our experimental results (Figure ).…”

“…An additional factor that can increase barriers for Ce 3þ 5d 1 thermal ionization in these compositions is an effective positive charge on Ce 3þ when it replaces Sr 2þ /Ca 2þ . 28 However, if improvements in thermal quenching were mainly due to an effective positive charge on Ce 3þ , there should be only small differences between O 2--rich and F --rich compositions, in contrast to our experimental results (Figure 2). Given the similar thermal quenching of Sr 3 AlO 4 F:Ce 3þ and the phosphors with lower levels of Si 4þ /O 2-(Figure 2), we initially propose that Ce 3þ ions in these phosphors require only one Fanion in their local coordination for significant improvements in their high-temperature performance.…”

Inhomogenous Broadening, Charge Compensation, and Luminescence Quenching in Ce3+-Doped Sr3AlO4F Phosphors

“…It is also possible that the relative energy position within the host bandgap of the Ce 3+ 4f 1 ground state can change for these various substitutions in Sr 3 AlO 4 F. This energy position for the Ce 3+ 4f 1 ground state relative to the host valence band can be determined by using the energy of the Ce 4+ -ligand charge transfer (CT) band. However, since the position of such CT transitions can be very sensitive to charge compensation and the local coordination environment, 1,29,30 further experiments and/or calculations will be necessary to further understand and assign the relationships between composition and Ce 3+ luminescence quenching in these hosts. Recent work within Cs 3 CoCl 5 -based phosphors using scanning transmission electron microscopy techniques 31…”

Blue Light-Emitting Diode Phosphors Based upon Oxide, Oxyhalide, and Halide Hosts

“…48 In principle, ionization-based quenching can also explain the different quenching temperatures between Sr 3 SiO 5 :Ce 3+ and Sr 2 REAlO 5 :Ce 3+ . In Sr 3 SiO 5 :Ce 3+ , Ce 3+ has an effective positive charge when replacing Sr 2+ which will increase the energy barrier for Ce 3+ (5d 1 ) ionization 49 versus Sr 2 REAlO 5 :Ce 3+ where there is less of an effective charge.…”