Formation process of core-shell structured Gd2O3:Yb3+/Er3+@SiO2.
X-ray diffraction patterns for the as-formed SiO2 (without annealing) (a) and Gd2O3:Yb3+/Er3+@SiO2 core-shell particles annealed at 900 °C (b). The standard datum for Gd2O3 (JCPDS No.12-0797) is also presented for comparison.
SEM micrographs of the as-formed SiO2 with different sizes (a)∼180 nm, (b) ∼120 nm, (c) ∼80 nm, (d) ∼30 nm and the SiO2 particles (a) coated with Gd2O3:15%Yb3+/1.5%Er3+ shells (e) as well as the energy dispersive X-ray spectrum (f) for the sample (e).
TEM micrographs of core-shell structured samples without (a) and with annealing treatment (b).
SEM micrographs of Gd2O3:Yb3+/Er3+@SiO2 core-shell particles (∼200 nm with the SiO2 core size of ∼180 nm) (a) pure Gd2O3:Yb3+/Er3+ particles (∼200 nm) (b) pure Gd2O3:Yb3+/Er3+ particles (∼130 nm) (c) as well as the UCL spectra of these three samples (d).
(a) Normalized UCL spectra of core-shell samples with different SiO2 core sizes. (b) The ratios of I G/I (R+G) and I R/I (R+G) change with the sizes of SiO2 core.
Double-logarithmic plots of emission intensity versus excitation power density for the core-shell samples with different SiO2 core sizes.
Energy level diagrams of Yb3+ and Er3+ ions, and possible UC processes.
Variation relationship of SiO2 core sizes and the specific areas of UCL shells in GYES samples (only outer surfaces of core-shell samples are considered. red line: shell thickness = 10 nm; black line: shell thickness = 15 nm).
Variation relationship of SiO2 core sizes and the specific areas of the UCL shells in GYES samples. (red line: both the outer and inner surfaces are considered; black line: only outer surfaces are considered. shell thickness = 15 nm).
Luminescence decay curves of Er3+ (λex = 980 nm, λem = 543 and 668 nm; represent the 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions, respectively) in core-shell samples with different SiO2 core sizes. Open circles: experimental data; solid lines: fitting results by I ( t ) = I0 exp(−t/τ).
Decay times of the 4 S 3/2 and 4 F 9/2 states of Er3+ in core-shell samples with different SiO2 core radii.
The molar ratios of TEOS:NH4OH:H2O for synthesizing SiO2 samples with different sizes.
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