YVnormalO4:normalBi3+,normalEu3+
nanoparticles were prepared by the wet chemical synthesis in various concentrations of sodium citrate,
15⩽xcit⩽90
, where
xcit
is the nominal molar percentage of citrate relative to the sum of metallic ions,
Y3+
,
Bi3+
, and
Eu3+
. Mean primary nanoparticle diameter and mean hydrodynamic size in the aqueous colloidal solution have minimum values, 21 and
36nm
, respectively, for the sample prepared at
xcit=50
. The transparency of the aqueous colloidal solution in the visible region increases with decreasing the mean hydrodynamic size, and the sample prepared at
xcit=50
shows the highest transparency.
YVnormalO4:normalBi3+,normalEu3+
nanoparticles show the characteristic photobleaching behavior and the photoreduction of
V5+
to
V4+
under the irradiation of near-UV light, where the fraction of photobleach becomes larger at large
xcit
. These results suggest that the citrate ion works not only as an effective dispersion agent, but also as a reducing agent against
V5+
of
YVnormalO4:normalBi3+,normalEu3+
.
Zn 2 GeO 4 :Mn 2þ nanophosphors are synthesized from germanium(IV) oxide and acetates of zinc and manganese(II) in a mixed solvent of water and diethylene glycol (DEG) by the solvothermal reaction at 200 °C for 2 h. Phase pure Zn 2 GeO 4 :Mn 2þ is obtained for the samples prepared at 0 e x DEG e 91.7, where x DEG is the volume percentage of DEG in the mixed solvent. The particle and crystallite sizes decrease with the increase in x DEG . The sample prepared at x DEG = 91.7 comprises the nanorods with 30.2 and 12.2 nm in mean length and width, respectively. The actual Mn concentration measured by X-ray fluorescence analysis increases with the increase in x DEG and approaches to the nominal concentration, 2.0 at %. The samples show green luminescence corresponding to the d-d transition of Mn 2þ under the irradiation of UV and near-UV light. The photoluminescence intensity reaches a maximum around x DEG ∼ 80. This is attributed to the competitive factors, the Mn concentration and the sizes of crystallites and particles.
YBO3:Ce3+,Tb3+ phosphor was prepared from rare earth oxides and boric acid by a solid state reaction. The phosphor absorbs near UV light through 4f–5d transitions of Ce3+, followed by broad emissions through 5d–4f transitions of Ce3+ and sharp emissions through 4f–4f transitions of Tb3+. Spectroscopic investigations for samples with various Ce3+ and Tb3+ concentrations reveal nonradiative energy transfer from Ce3+ to Tb3+. Emission color of the YBO3:Ce3+,Tb3+ varies from blue (0.163, 0.019) to green (0.321, 0.585) depending on the Ce3+ and Tb3+ concentrations. The optimized green-emitting Y0.82Ce0.03Tb0.15BO3 phosphor has an emission color of (0.309, 0.547) with an external quantum efficiency of 76.7%. The photoluminescence intensity of this phosphor at 150°C keeps 87% of its intensity at room temperature, showing sufficient thermal stability for white light emitting diode applications.
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