Enhancing the Up-Conversion Emission of ZrO₂:Er³⁺ Nanocrystals Prepared by a Micelle Process

Abstract

Erbium doped ZrO 2 nanocrystals ranging from 30 to 80 nm in size were prepared by a sol-gel process with the presence of cationic (CTAB) and nonionic (PLURONIC P-127) surfactants, and the up-conversion emission was characterized. A strong green emission was produced by the transition 2 H 11/2 + 4 S 3/2 f 4 I 15/2 and enhanced 1 order of magnitude with the presence of PLURONIC P-127 at a molar ratio Mrp ) 0.0082 annealed 5 h at 1000 °C. A molar ratio of Mrc ) 0.2 CTAB annealed 0 min at 1000 °C induced an increment of 300% of the signal emitted. In both cases the enhancement was partly attributed to the high content of monoclinic phase and crystallite size. However, the dominant parameter for the enhancement of the luminescence was the elimination of residual contaminants and defects produced for surface recombination.

Surfactant effect on the upconversion emission and decay time of ZrO2:Yb-Er nanocrystals

“…The introduction of surfactant reduces the residual OH À component, as can be observed in the FTIR spectrum displayed in Fig. 3 and was reported recently [28][29][30]. The surfactant works as a dispersing agent and its function is to weaken the organic bond.…”

“…4. Such bands are assigned to 2 H 11/2 + 4 S 3/2 -4 I 15/2 and 4 F 9/2 -4 I 15/2 transitions of the Er ion, respectively and are the result of the absorption of two photons either from the pumping or from the energy transfer between neighboring ions [30]. Upconverted emission depends on the ion concentration, for Er-doped nanocrystals is strongly dominated by the green band, the red band being only 5% of the total signal emitted.…”

“…With that concentration, the integrated signal obtained by annealing for 5 h at 1000 1C is notably higher (97%) than the signal obtained without the surfactant for samples annealed for 5 h and 70% for samples annealed for 0 min. Such a strong increment in the emitted signal is related with the reduction of organic impurities as a result of the annealing time increment (0 min to 5 h) and the use of Pluronic F-127 during the synthesis process [30]. The former controls the crystallite size and the surfactant disperses nanocrystals, reducing the agglomeration and absorption of impurities on the crystallite surface.…”

Labeling of HeLa cells using ZrO 2 : Yb 3 + - Er 3 + nanoparticles with upconversion emission

“…Green and red emission bands are assigned to 2 H 11∕2 þ 4 S 3∕2 → 4 I 15∕2 and 4 F 9∕2 → 4 I 15∕2 transitions of the Er 3þ ion, and they are caused by the successive absorption of two photons after energy transfer from Yb 3þ ions. 59 According to previous works, the emission is predominantly red because OH groups have a vibrational energy (3000 to 4000 cm −1 ) which produces nonradiative relaxations from the mixed level 2 H 11∕2 þ 4 S 3∕2 toward the 4 F 9∕2 level. 71 In our case, the presence of OH moieties in all samples is corroborated by the FTIR spectra in Fig.…”

“…2(b) is an SEM image, which shows well-dispersed nanocrystals, and this was caused by the introduction of PF127 during the synthesis process. 59 The size and dispersion of the co-doped ZrO 2 ∶Yb 3þ -Er 3þ nanocrystals was controlled from the nucleation process due to the presence of ammonia, water/ethanol, and surfactant Pluronic PF127. 56 To promote the efficient internalization in HeLa cells, it is important to have particles in the nanoscale size regime.…”