Yida Wang

Coupling of Ag Nanoparticle with Inverse Opal Photonic Crystals as a Novel Strategy for Upconversion Emission Enhancement of NaYF4: Yb(3+), Er(3+) Nanoparticles.

Rare-earth-ion-doped upconversion (UC) nanoparticles have generated considerable interest because of their potential application in solar cells, biological labeling, therapeutics, and imaging. However, the applications of UC nanoparticles were still limited because of their low emission efficiency. Photonic crystals and noble metal nanoparticles are applied extensively to enhance the UC emission of rare earth ions. In the present work, a novel substrate consisting of inverse opal photonic crystals and Ag nanoparticles was prepared by the template-assisted method, which was used to enhance the UC emission of NaYF4: Yb(3+), Er(3+) nanoparticles. The red or green UC emissions of NaYF4: Yb(3+), Er(3+) nanoparticles were selectively enhanced on the inverse opal substrates because of the Bragg reflection of the photonic band gap. Additionally, the UC emission enhancement of NaYF4: Yb(3+), Er(3+) nanoparticles induced by the coupling of metal nanoparticle plasmons and photonic crystal effects was realized on the Ag nanoparticles included in the inverse opal substrate. The present results demonstrated that coupling of Ag nanoparticle with inverse opal photonic crystals provides a useful strategy to enhance UC emission of rare-earth-ion-doped nanoparticles.

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.

Upconversion emission enhancement mechanisms of Nd3+-sensitized NaYF4:Yb3+,Er3+ nanoparticles using tunable plasmonic Au films: plasmonic-induced excitation, radiative decay rate and energy-transfer enhancement

The upconversion luminescence (UCL) of rare earth ion-doped nanoparticles excited at 808 nm is more suitable for biological applications than those excited at 980 nm, as the former avoids overheating of biological tissues caused by 980 nm excitation light. However, one of the major challenges limiting the application of UCL of rare earth ion-doped nanoparticles excited at 808 nm is their low UCL efficiency. In this work, tunable plasmonic Au films were used to improve the UCL of Nd3+-sensitized NaYF4:Yb3+,Er3+ nanoparticles. The results show that the enhancement factors and mechanisms of the UCL of Nd3+-sensitized nanoparticles are associated with the tunable plasmonic properties of Au films. The maximum enhancement factors of green and red UCL of NaYF4:Nd3+,Yb3+,Er3+ nanoparticles excited at 808 nm are 6 and 5.8 on the Au film with ultra-broad plasmonic absorption band, respectively. A differentiation of UCL-enhanced mechanisms of NaYF4:Nd3+,Yb3+,Er3+ nanoparticles on tunable plasmonic Au films was observed. The enhanced UCL of NaYF4:Nd3+,Yb3+,Er3+ nanoparticles on the Au film with a narrow plasmonic absorption peak was due to the enhanced excitation field. The enhanced excitation field and energy-transfer enhancement was responsible for the UCL enhancement of NaYF4:Nd3+,Yb3+,Er3+ nanoparticles on the Au film with ultra-broad plasmonic absorption.

Upconversion emission enhancement by porous silver films with ultra-broad plasmon absorption

Abstract: Surface plasmon effects of Ag nanostructures are being extensively applied to enhance upconversion (UC) luminescence properties of rare-earth-ion-doped nanoparticles. However, the plasmonic absorption bands from various Ag nanostructures are generally located at a visible region that cannot couple effectively with the 980 nm near infrared excitation light, resulting in a smaller UC emission enhancement factor. In this paper, we present a facile method to fabricate the porous Ag films with tunable and ultra-broad surface plasmonic absorption by using a polystyrene microsphere as a hard template, and then investigate the influence of tunable surface plasmonic absorption (SPA) on the UC emission. About 10 and 60-fold UC emission enhancement of NaYF4: Yb3+, Er3+ nanoparticles was obtained on the Ag films with narrow and ultra-broad SPA ranging from 350 to 1400 nm, respectively. The UC emission increases 60 fold at the surface of porous Ag film with the ultra-broad plasmonic absorption, which is attributed to efficient coupling between the ultra-broad SPA and the 980 nm near infrared excitation light and UC emission. The results demonstrate Ag film with ultra-broad plasmonic absorption is more appropriate as a substrate for the enhancement of UC emission in comparison with the narrow plasmonic absorption Ag film.

Tunable and ultra-broad plasmon enhanced upconversion emission of NaYF4:Yb3+, Er3+ nanoparticles deposited on Au films with papilla Au nanoparticles

Rare earth ions doped upconversion nanoparticles have broad applications ranging from biological imaging to solar energy conversion. However, the application of upconversion nanoparticles has been limited due to their low upconversion efficiencies. In this paper, two kinds of Au films with tunable and broad surface plasmonic absorptions were used to enhance the upconversion emission of NaYF4:Yb3+, Er3+ nanoparticles, respectively. The results demonstrated that the upconversion enhancement is highly dependent on the topography of Au films. About 77 and 40-fold enhancement were obtained for the green and red UC emissions of NaYF4:Yb3+, Er3+ nanoparticles on the irregular and random Au particles. About 121 and 78-fold enhancement were obtained for the green and red UC emissions of NaYF4:Yb3+, Er3+ nanoparticles on continuous Au films with papilla Au nanoparticles, respectively. In contrast to that of NaYF4:Yb3+, Er3+ nanoparticles deposited on quartz substrate, and the corresponding UC efficiency of NaYF4:Yb3+, Er3+ nanoparticles on irregular and random Au particles and continuous Au films with papilla Au nanoparticles increased by 50% and 100%, respectively. The enhancement of UC emission may be attributed to the increase of radiative decay rate and the enhancement of excitation field.

Upconversion Emission Modification and White Light Generation in NaYF 4 :Yb 3+ , Er 3+ , Tm 3+ Nanocrystals/Opal Photonic Crystal Composites

In this paper, we fabricated NaYF 4:Yb³⁺, Er³⁺, Tm³⁺ nanocrystal/opal photonic crystal composites by depositing NaYF 4:Yb³⁺, Er³⁺, Tm³⁺ nanocrystals on the surface of opal photonic crystals, and we investigated the influence of photonic bandgaps on upconversion (UC) emission properties of NaYF 4:Yb³⁺, Er³⁺, Tm ³⁺ nanocrystals. When the photonic bandgaps overlapped with the UC emission bands of NaYF 4:Yb³⁺, Er³⁺, Tm³⁺ nanocrystals on the opal photonic crystal surfaces, the suppression or enhancement of UC emissions was observed due to the Bragg reflection effect of photonic crystal, resulting in the modification of red, green, and blue UC emissions. Thus, white UC emission was realized.