15 “Polymer–Oxide” Micro-/Nanocomposites: Background and Promises
269
consist of several overlapping bands lying in the ranges ∼ 250–350, 300–425, 350–
475, and 425–525 nm. Excitation spectra change if wavelength of the PL registration
(λ reg ) changes. Thus, short wavelength band in excitation (250–350 nm) vanishes if
λ reg changes from 580 to 460 nm (Fig. 15.12, curves 1, 2). The same was observed
for excitation of luminescence of the 100-La 0.7 Sm 0.3 VO 4 composite. We see that
only 300–450 nm range of excitation is actual, while other ones diminished (Fig.
15.12, curve 3).
Our results revealed also correspondence between components in luminescence
and excitation spectra and confirmed that several origins contribute to the luminescence of cellulose matrix. Namely, we can state that the shortwave side of the MCC
luminescence is excited in the bands ranging from 300 to 450 nm. We state also that
both heating and oxide particle action on these sources are selective and different,
which may be due to the features of molecular relaxations and due to features of the
molecular anions of oxides (vanadate, VO 4
3− ; phosphate, PO 4
3− ; or molybdate,
MoO 4
− ) binding with molecular groups on the surface of cellulose microfibrils.
When the PL is registered near the narrow PL lines, new details of the excitation
spectra have been measured (Fig. 15.12, curves 3–5). No doubt, these additives, as
well as narrow lines in the PL spectra, are related with absorption and radiation
transitions in the f n -shells of Sm 3+ or Eu 3+ ions and O 2− ➔ RE 3+ charge-transfer
transitions in oxide component of the composites. Really, the positions of these
groups of lines, their shapes, and their intensity coincide with excitation and
luminescence data for corresponding “free” powder oxides taken by us recently
[70–71].
As for composites containing Sm 3+ ions, it is easy to conclude that additive
narrow PL lines and lines in excitation spectra are related with f –f transitions in the
electronic shell of the Sm 3+ ions. In fact, the positions of these groups of lines, their
shapes, and distribution of their intensity coincide with absorption and emission
lines of the Sm 3+ ions in various crystalline [71, 80–82], glasslike hosts [83, 84],
and liquids [85]. So, we can state that observed PL groups of lines are due to
radiation transitions 4 G 5/2 ➔ 6 H 9/2 , 6 H 7/2 , 6 H 5/2 , from excited 4 G 5/2 level to the
lowest levels of the ground 6 H state.
As for composites containing Eu 3+ ions, a comparison of described emission and
excitation spectra with the corresponding spectra of the free K 2 Eu(MoO 4 )(PO 4 )
or La 1−x Eu x VO 4 powder compounds show that the observed PL lines have to be
ascribed to the 5 D 0 ➔ 7 F J (J = 1 ÷ 4) radiation transitions in the inner f–f electronic
shells of the Eu 3+ ions which are in the composition of oxide compounds [70, 71].
Changes of the shape and decrease of MCC host PL intensity, when content
of the oxide increases, can be related with influence of the oxide particles on the
morphology and dynamics of various cellulose molecular groups located on the
microfibril surface. It is worth to note that distributions of intensity of the Sm 3+ and
Eu 3+ ion PL lines differ from one corresponding to “free” oxide powders [70, 71].
We have known that these RE 3+ ions locate in the volume and on the surface of used
oxide particles [70, 71]. Positions of the lines in the PL and excitation spectra of the
Sm 3+ and Eu 3+ ions noted “at surface” and “in volume” types of ions are different.
Obviously, “at surface” ions, in the first place, have been sensitive to the influence of
269
consist of several overlapping bands lying in the ranges ∼ 250–350, 300–425, 350–
475, and 425–525 nm. Excitation spectra change if wavelength of the PL registration
(λ reg ) changes. Thus, short wavelength band in excitation (250–350 nm) vanishes if
λ reg changes from 580 to 460 nm (Fig. 15.12, curves 1, 2). The same was observed
for excitation of luminescence of the 100-La 0.7 Sm 0.3 VO 4 composite. We see that
only 300–450 nm range of excitation is actual, while other ones diminished (Fig.
15.12, curve 3).
Our results revealed also correspondence between components in luminescence
and excitation spectra and confirmed that several origins contribute to the luminescence of cellulose matrix. Namely, we can state that the shortwave side of the MCC
luminescence is excited in the bands ranging from 300 to 450 nm. We state also that
both heating and oxide particle action on these sources are selective and different,
which may be due to the features of molecular relaxations and due to features of the
molecular anions of oxides (vanadate, VO 4
3− ; phosphate, PO 4
3− ; or molybdate,
MoO 4
− ) binding with molecular groups on the surface of cellulose microfibrils.
When the PL is registered near the narrow PL lines, new details of the excitation
spectra have been measured (Fig. 15.12, curves 3–5). No doubt, these additives, as
well as narrow lines in the PL spectra, are related with absorption and radiation
transitions in the f n -shells of Sm 3+ or Eu 3+ ions and O 2− ➔ RE 3+ charge-transfer
transitions in oxide component of the composites. Really, the positions of these
groups of lines, their shapes, and their intensity coincide with excitation and
luminescence data for corresponding “free” powder oxides taken by us recently
[70–71].
As for composites containing Sm 3+ ions, it is easy to conclude that additive
narrow PL lines and lines in excitation spectra are related with f –f transitions in the
electronic shell of the Sm 3+ ions. In fact, the positions of these groups of lines, their
shapes, and distribution of their intensity coincide with absorption and emission
lines of the Sm 3+ ions in various crystalline [71, 80–82], glasslike hosts [83, 84],
and liquids [85]. So, we can state that observed PL groups of lines are due to
radiation transitions 4 G 5/2 ➔ 6 H 9/2 , 6 H 7/2 , 6 H 5/2 , from excited 4 G 5/2 level to the
lowest levels of the ground 6 H state.
As for composites containing Eu 3+ ions, a comparison of described emission and
excitation spectra with the corresponding spectra of the free K 2 Eu(MoO 4 )(PO 4 )
or La 1−x Eu x VO 4 powder compounds show that the observed PL lines have to be
ascribed to the 5 D 0 ➔ 7 F J (J = 1 ÷ 4) radiation transitions in the inner f–f electronic
shells of the Eu 3+ ions which are in the composition of oxide compounds [70, 71].
Changes of the shape and decrease of MCC host PL intensity, when content
of the oxide increases, can be related with influence of the oxide particles on the
morphology and dynamics of various cellulose molecular groups located on the
microfibril surface. It is worth to note that distributions of intensity of the Sm 3+ and
Eu 3+ ion PL lines differ from one corresponding to “free” oxide powders [70, 71].
We have known that these RE 3+ ions locate in the volume and on the surface of used
oxide particles [70, 71]. Positions of the lines in the PL and excitation spectra of the
Sm 3+ and Eu 3+ ions noted “at surface” and “in volume” types of ions are different.
Obviously, “at surface” ions, in the first place, have been sensitive to the influence of