Shenfeng Lai

Photoluminescence enhancement of Eu3+ ions by Ag species in SiO2 three-dimensionally ordered macroporous materials

The existing states of silver depend on the sintering temperature of SiO2 three-dimensionally ordered macroporous (3DOM) materials. Several species related to silver (Ag+ ions, Ag+–Ag+ and Ag nanoparticles) were demonstrated in SiO2 3DOM materials prepared at 550 °C. Only Ag nanoparticles were observed in SiO2 3DOM materials prepared at 750 °C. The influence of silver species on the photoluminescence properties of Eu3+ was investigated systematically in SiO2 3DOM materials. The results show that photoluminescence enhancement of Eu3+ ions was induced by Ag species in SiO2 3DOM materials. For the SiO2 3DOM materials prepared at 550 °C, the enhancement of Eu3+ luminescence is attributed to energy transfer from Ag+–Ag+ to Eu3+ under excitation at 345 or 280 nm, while the luminescence enhancement of Eu3+ is due to energy transfer from isolated Ag+ to Eu3+ under excitation at 245 nm. For the SiO2 3DOM materials prepared at 750 °C, the luminescence of Eu3+ was enhanced due to the plasmon resonance effect of Ag nanoparticles.

Preparation and upconversion emission modification of crystalline colloidal arrays and rare earth fluoride microcrystal composites.

In this paper, highly ordered crystalline colloidal arrays containing rare earth fluoride microcrystals were fabricated. The upconversion emission property of rare earth fluoride microcrystals in crystalline colloidal arrays was studied and modified. A significant suppression and enhancement of the upconversion emission from the rare earth fluorides can be observed in the regions of the photonic band gap and its band edge, respectively. The suppression or enhancement factor was shown to be related to the ordered degree of the crystalline colloidal arrays and is critical in the preparation of upconversion displays and low-threshold lasers.

Investigation on existing states and photoluminescence property of silver in the SiO2 three-dimensionally ordered macroporous materials

The photoluminescence properties of silver species, including Ag+, Ag+–Ag+, Ag0, and Ag nanoparticles in various matrices, such as gel and glass have been extensively reported. In the present study, we present the preparation of silver including SiO2 three-dimensionally ordered macroporous (3DOM) materials and investigate the existing states and photoluminescence property of silver in the SiO2 3DOM materials. The results show that only Ag+ ions exist in the SiO2 3DOM materials sintered at temperature below 400 °C. With the increasing sintering temperature, the Ag+ ions gradually transform into Ag+–Ag+, where simultaneously, a part of Ag+–Ag+ transform into Ag nanoparticles. The Ag+–Ag+ and Ag nanoparticles are formed in the SiO2 3DOM materials sintered at temperature from 450 to 650 °C. Finally, only Ag nanoparticles occur in the SiO2 3DOM materials prepared at 750 °C. The formation mechanisms of Ag species were discussed in the SiO2 3DOM materials.

Enhancement of near-infrared to near-infrared upconversion emission in the CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opals.

In this Letter, CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opal with near-infrared to near-infrared upconversion emission was prepared by polystyrene colloidal crystal templates, and the influence of photonic bandgap on the upconversion emission was investigated. Comparing with the reference sample, suppression of the blue or red upconversion luminescence was observed in the inverse opals. It is interesting that the near-infrared upconversion emission located at about 803 nm was enhanced due to the inhibition of visible upconversion emission in the inverse opals. Additionally, the variety of upconversion emission mechanisms was observed and discussed in the CeO₂: Er³⁺, Tm³⁺, Yb³⁺ inverse opals.

UPCONVERSION LUMINESCENCE ENHANCEMENT OF NaYF4:Yb3+, Er3+ NANOPARTICLES ON INVERSE OPAL SURFACE

LaPO4 inverse opal photonic crystals with different photonic band gaps were fabricated by template-assisted method. The Yb3+/Er3+ co-doped NaYF4 nanoparticles were deposited on the surfaces of the inverse opals, and their up-conversion emission properties were investigated. The upconversion emissions of Yb3+/Er3+ co-doped NaYF4 nanoparticles on the inverse opal surfaces have been enhanced when the upconversion emission bands of the nanoparticles are in the range of photonic band gaps of the inverse opals, which is attributed to an efficient and selective reflection of photonic band gaps.

Investigation of upconversion and near infrared emission properties in CeO 2 : Er 3+ , Yb 3+ inverse opals

The upconversion emission of rare earth ions can be modified in photonic crystals, however, the influence of upconversion emission modification of rare earths on near infrared emission has not been investigated yet in the photonic crystals. In the paper, CeO₂: Er³⁺, Yb³⁺ inverse opals with the photonic band gaps at 545, 680 and 450 nm were prepared by polystyrene colloidal crystal templates. The upconversion and the near infrared emission properties of Er³⁺ ions were systematically investigated in the CeO₂: Er³⁺, Yb³⁺ inverse opals. Comparing with the reference sample, significant suppression of both the green and red upconversion luminescence of Er³⁺ ions were observed in the inverse opals. It is interesting that the infrared emission located at 1,560 nm was enhanced due to inhibition of upconversion emission in the inverse opals. Additionally, mechanism of upconversion emission of the inverse opal was discussed. The photon avalanche upconversion process is observed.

PHOTONIC CRYSTAL SURFACE ENHANCED UPCONVERSION EMISSION OF YF3:Yb3+, Er3+ NANOPARTICLES

The opal photonic crystals made of polystyrene microspheres with 155, 230, 270 or 410 nm in diameter were used to enhance upconversion (UC) emission of YF3:Yb3+, Er3+ nanoparticles, respectively. The red or green UC emission of YF3:Yb3+, Er3+ nanoparticles can be selectively enhanced when the red or green UC emission wavelength overlapped with the photonic bandgaps of opals, which is attributed to Bragg reflection of photonic bandgap. In addition, when the 980 nm excitation light wavelength was in the region of the photonic bandgap, red and green UC emissions of YF3:Yb3+, Er3+ nanoparticles were enhanced due to the enhancement of excitation field.

Continuous modification of upconversion luminescence of fluorescent dye in the crystalline colloidal arrays

The crystalline colloidal arrays with controllable photonic bandgaps were prepared by the change of volume fraction of the polystyrene microspheres. Upconversion emission property of fluorescent dye has investigated in crystalline colloidal array, and continuous modification of the upconversion emission of fluorescent dye was observed. A significant suppression of upconversion emission of dye in the range of the photonic bandgap as well as enhancement at the bandgap edge was obtained in the crystalline colloidal arrays. In addition, upconversion emission of dye was also enhanced when the excited light overlapped with the long or short bandgap edge of the crystalline colloidal arrays, which is due to slow photons effect near the edges of a photonic bandgap. The continuous modification and enhancement of upconversion emission may be important for the development of low-threshold upconversion lasers and displays.

Upconversion emission properties of CeO2: Tm3+, Yb3+ inverse opal photonic crystals

The ordered and disordered templates were assembled by vertical deposition of polystyrene microspheres. The CeO2: Tm3+, Yb3+ precursor solution was used to infiltrate into the voids of the ordered and disordered templates, respectively. Then the ordered and disordered templates were calcined at 950°C in an air furnace, and the CeO2: Tm3+, Yb3+ inverse opals were obtained. The upconversion emissions from CeO2: Tm3+, Yb3+ inverse opals were suppressed due to the photon trapping caused by Bragg reflection of lattice planes when the upconversion emission band was in the range of the photonic band gaps in the inverse opals.