Chloroform- and Water-Soluble Sol–Gel Derived $\hbox{Eu}^{+++}/\hbox{Y}_{{\rm 2}}\hbox{O}_{{\rm 3}}$ (Red) and $\hbox{Tb}^{+++}/\hbox{Y}_{{\rm 2}}\hbox{O}_{{\rm 3}}$ (Green) Nanophosphors: Synthesis, Characterization, and Surface Modification

Eu
⁺⁺⁺
and Tb
⁺⁺⁺
ions have been incorporated into nanodimensional yttrium oxide host matrices via a sol-gel process using Y
₅
O(OPr
ⁱ
)
₁₃
as precursor (OPr
ⁱ
= isopropoxy). The as-synthesized white powders have been annealed at different temperatures. Photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) have been used as tools for documenting the characteristics of these powders. For Eu
⁺⁺⁺
-doped powders, a comparison of the Eu
⁺⁺⁺
,
⁵
D
₀
rarr
⁷
F
₁
, and
⁵
D
₀
rarr
⁷
F
₂
peak intensities in the emission spectra reveals that the dopant ions are occupying unsymmetrical sites in the host yttrium oxide in all the samples. For Tb
⁺⁺⁺
-doped powders, the characteristic terbium
⁵
D
₃
rarr
⁷
F
_n
and
⁵
Drarr
⁷
F
_n
(
n
= 2-6) transitions were visible only in the samples that had been annealed above 500degC. Samples of the doped particle powders were suspended in chloroform by fragmenting the powder with and without sonification under the presence of trioctylphosphine oxide, or a mixture of oleic acid and dioctyl ether. The resulting clear colorless (for Eu
⁺⁺⁺
) and light green translucent (for Tb
⁺⁺⁺
) solutions of the suspended particles showed red and green luminescence upon UV excitation, respectively. In addition, suspension in water has been achieved by fragmenting the powder in the presence of dichloroacetic acid. Transmission electron micrograph investigation of the soluble particles shows single dispersed particles along with agglomerates. The changes in the luminescence due to fragmentation of the particle powder and due the influence of the surfactant of the suspended colloidal particles are discussed.