•Dy3 + and Eu3 + single doped and co-doped tellurite glasses were prepared.•Tunable luminescence was obtained by the energy transfer from the Dy3 + to Eu3 +.•By coupling Dy3 + and Eu3 + co-doped glasses with UV or blue chip to construct the WLEDThe glasses including phosphor particles were prepared and developed to avoid the poor thermal stability of the organic encapsulants in the commercially dominant YAG: Ce3 + phosphor converted WLEDs. However, the preparation of glasses including phosphor particles with the white emission is relative complex and difficult. In this work, the tellurite glasses single doped and co-doped with Dy3 + and Eu3 + were prepared, and their photoluminescence properties were investigated. The results demonstrated that the tellurite glasses single doped with Dy3 + and Eu3 + exhibited the yellow and red emission under the excitation of UV and blue light, respectively. For the tellurite glasses co-doped with Dy3 + and Eu3 +, the energy transfer from the Dy3 + and Eu3 + ions was observed due to the electric dipole-dipole interaction, and the tunable luminescence was obtained by changing the Eu3 + concentration. The light-emitting diodes were constructed by coupling Dy3 + and Eu3 + co-doped tellurite glasses with the UV or blue chip, and the chromaticity coordinate of such LEDs can be well tuned to white light region. These results indicated that the Dy3 + and Eu3 + co-doped tellurite glasses can act as a promising candidate for the blue and UV converted WLEDs.

White or tunable photoluminescence of phosphors is of great significance for their practical applications in the light-emitting diodes. In this work, Ba2Y(BO3)2Cl:Bi3+,Eu3+ phosphors were fabricated, and their photoluminescence properties were investigated. Three difference luminescence peaks located at 366, 410, and 490 nm were observed in the single Bi3+-doped Ba2Y(BO3)2Cl phosphor under the excitation of ultraviolet light attributed to three various Bi3+ sites occupied in the Ba2Y(BO3)2Cl host. By tuning the excitation wavelength from three various Bi3+ sites, the tunable luminescence properties were obtained. The energy transfer from Bi3+ at various sites to Eu3+ were observed in the Ba2Y(BO3)2Cl:Bi3+,Eu3+ phosphors by an electric dipole–dipole interaction. The tunable and white luminescence was obtained by changing the Eu3+ concentration or excitation wavelength. The light-emitting diodes with the white light emission were constructed by coupling Bi3+ and Eu3+ codoped Ba2Y(BO3)2Cl phosphors with the UV chip, which indicated that the Bi3+ and Eu3+ codoped Ba2Y(BO3)2Cl phosphors can act as a promising candidate for the UV converted WLEDs.

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.

Comprehensive investigations of near infrared (NIR) downshift and visible upconversion luminescence (UCL) mechanisms were carried out for Yb3+ single-doped and Er3+,Yb3+ co-doped SiO2 inverse opals under excitation at 256, 378, 520 and 980 nm. NIR emission at 976 nm from the Yb3+–O2− charge transfer state and UCL emission at 500 nm due to the cooperative emission of two Yb3+ ions were observed in SiO2:Yb3+ inverse opal upon excitation at 256 and 980 nm, respectively. The cooperative UCL of two Yb3+ ions was suppressed due to the photon trap created by the photonic band gap. For the SiO2:Er3+,Yb3+ inverse opals, NIR emission of Yb3+ at 976 nm and of Er3+ at 1534 nm were observed upon excitation at 256, 378 and 520 nm, respectively. Upon excitation at 378 and 520 nm, the 976 nm NIR emission of Yb3+ does not arise from (2H11/2/4S3/2) + 2Yb3+(2F7/2) → Er3+(4I15/2) + 2Yb3+(2F5/2) traditional quantum cutting. The NIR emission of Yb3+ at 976 nm may be due to the Er3+(2H11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I11/2) cross-relaxation energy transfer process upon excitation at 520 nm. The NIR emission of Yb3+ at 976 nm may arise from the cross-relaxation energy transfer of Er3+(4G11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4F9/2) and Er3+(4F9/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I13/2) upon excitation at 378 nm.

Photonic crystal heterostructures composed of YbPO4:Er3+ inverse opal and polystyrene opal were prepared via a template-assisted process, which exhibited two photonic band gaps. The microstructure, phase and optical properties of photonic crystal heterostructures were investigated by x-ray diffraction, scanning electron microscopy, fluorescence spectroscopy, absorption spectroscopy, fluorescence lifetime, etc. The upconversion emission suppression caused by single photonic band gap from the following YbPO4:Er3+ inverse opal or the upper opal was observed. The upconversion luminescence was strongly suppressed due to the two photonic band gap overlapping effect caused by the following YbPO4:Er3+ inverse opal or the upper opal. The modified mechanisms of upconversion luminescence were discussed by the upconversion luminescence lifetime of YbPO4:Er3+ photonic crystal heterostructures. The results demonstrated the modified upconversion luminescence is attributed to the photon trapping caused by Bragg reflection of photonic crystal heterostructures.Download high-res image (380KB)Download full-size image

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.

•SiO2:Yb3 +, Tb3 + inverse opals containing gold nanoparticles were synthesized.•Effect of Au nanoparticles on UC emission of SiO2 inverse opal was studied.•Enhanced UC emission of SiO2 inverse opal was obtained by Au nanoparticles.The SiO2:Yb3 +, Tb3 + inverse opal photonic crystals containing gold nanoparticles were prepared by the self-assembly technique combined with a sol–gel method, and their up-conversion luminescence properties have been investigated under the excitation of 980 nm. The upconversion emission bands from the Tb3 + ions were located at 489, 544, 585 and 622 nm in the SiO2:Yb3 +, Tb3 + inverse opals. The influence of Au nanoparticles on the upconversion emission was observed in the SiO2:Yb3 +, Tb3 + inverse opals. The upconversion emission of SiO2:Yb3 +, Tb3 + inverse opals was enhanced, which is from the population increasing of 5D4 luminescent level of Tb3 + ions induced by surface plasmon effects of Au nanoparticles.

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.

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: Yb3+, Er3+ nanoparticles. The red or green UC emissions of NaYF4: Yb3+, Er3+ 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: Yb3+, Er3+ 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.Keywords: enhancement; NaYF4: Yb3+, Er3+ nanoparticles; SiO2 inverse opal including Ag nanoparticles; surface plasmon resonance; upconversion emission

The three-dimensional ordered macroporous CeO2:Yb,Er materials were prepared, and the influence of doping concentration of Yb3+ or Er3+ ions on upconversion property was investigated. Green and red upconversion emissions were observed under the excitation of 980 nm at room temperature. It was found that the ratio of red to green upconversion emission intensity increased with increasing of concentration of the Yb3+ or Er3+ ions in the three-dimensional ordered macroporous CeO2:Yb,Er materials. When the concentration of Yb3+ was 10 mol.%, pure red upconversion emission was obtained. The varied mechanism of ratio of red to green upconversion emission intensity was discussed with the concentration of Yb3+ or Er3+ ions.The three-dimensional ordered macroporous CeO2:Yb,Er materials were prepared, and color tunbility of upconversion emission can be obtained by change of Yb3+ or Er3+ ions doping concentration

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.

•Three dimensionally ordered macroporous (3DOM) materials•SiO2:Tb3 + 3DOM materials including Ag nanoparticles•Ag nanoparticles can enhance the light emission of SiO2:Tb3 + 3DOM materials.•Luminescence enhancement mechanisms of Ag nanoparticles were discussed.The SiO2:Tb3 + three dimensionally ordered macroporous (3DOM) composites including Ag nanoparticles were successfully synthesized by colloidal crystal template method. The influence of Ag nanoparticles on photoluminescence property of SiO2:Tb3 + 3DOM material was investigated. The results indicate that typical emission bands at 489, 543, 587 and 623 nm from Tb3 + were observed in the SiO2:Tb3 + 3DOM materials under the excitation of 235 nm. The Ag nanoparticles can greatly enhance the light emission from Tb3 + in SiO2:Tb3 + 3DOM material, which was attributed to the increased radiative decay rates of Tb3 + caused by Ag nanoparticles.

•Three-dimensional order macroporous (3DOM) Bi2Ti2O7:Er3+, Yb3+,Li+ was prepared.•Effect of Li+ on upconversion emission of 3DOM Bi2Ti2O7: Er3+, Yb3+ was observed.•Li+ ions doping enhanced upconversion emission of 3DOM Bi2Ti2O7: Er3+, Yb3+.Three-dimensional ordered macroporous (3DOM) Bi2Ti2O7: Er3+,Yb3+ materials with Li+ doping were prepared by a template-assisted method, and the influence of Li+ ions on upconversion (UC) luminescence properties of 3DOM Bi2Ti2O7: Er3+,Yb3+ was investigated. Green and red UC emissions were observed in the 3DOM Bi2Ti2O7: Er3+,Yb3+ under the excitation of 980 nm, and doping with Li+ ions could enhance the green and red UC emissions of 3DOM Bi2Ti2O7: Er3+,Yb3+. In addition, the reasons of UC emission enhancement were discussed.

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.

Metal nanoparticle plasmons or the photonic crystal effect are being widely used to modify luminescence properties of materials. However, coupling of surface plasmons with photonic crystals are seldom reported for enhancing luminescence of materials. In this paper, a new method for upconversion emission enhancement of rare-earth doped nanoparticles is reported, attributed to the coupling of surface plasmons with photonic band gap effects. Opal/Ag hybrid substrates were prepared by depositing Ag nanoparticles on the top layer of opals by magnetron sputtering. The selective enhancement of red or green upconversion emission of NaYF4:Yb3+,Er3+ nanoparticles on the opal/Ag hybrid substrates is attributed to the coupling effect of surface plasmons and Bragg reflection of the photonic band gap. In addition, the upconversion emission enhancement of NaYF4:Yb3+,Er3+ nanoparticles on the opal/Ag hybrid substrate is attributed to the excitation enhancement was obtained when the excitation light wavelengths overlap with the photonic band gaps of opal/Ag hybrid substrates. We believe that these enhancement effects based on the coupling of metal nanoparticles with the photonic band gap could be extended to other light-emitting materials, which may result in a new generation of lighting devices.

A new method for enhancing the upconversion (UC) emission of rare-earth doped nanoparticles is reported, in which Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles are deposited on to the surface of photonic crystal (PC) films. The UC emission of the Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles on the PC surface was notably enhanced when the UC emission bands of the Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles were within the range of the photonic band gap of the PCs, indicating that the PCs were efficient and selective reflection mirrors. The results show that PCs may have potential applications in UC optoelectronics and lighting devices.

In this article, we fabricated Y2Ti2O7: Yb, Er, Tm upconversion inverse opal photonic crystals with energy transfer between Er3+ and Tm3+, and investigated the influence of the photonic band gap on the energy transfer between Tm3+ and Er3+. It is interesting that strong modification of the steady state upconversion emission spectra is observed, and the green or red upconversion emission from Er3+ was suppressed in the inverse opal. More significantly, the energy transfer between Tm3+ and Er3+ is enhanced by suppression of the red upconversion emission of Er3+, thus the blue upconversion emission from Tm3+ is considerably improved in the inverse opals. Additionally, the mechanisms for upconversion emission of the Y2Ti2O7: Yb, Er, Tm inverse opal are discussed. We believe that the present work will be valuable for the foundational study of upconversion emission modification and the application of upconversion displays and short wavelength upconversion lasers.

The SiO2: Tb, Yb inverse opals with photonic band gap at 465 or 543 nm were prepared, and an effect of photonic band gap on upconversion spontaneous emission from Tb3+ was investigated. The results show that the photonic band gap has a significant influence on the upconversion emission of the SiO2: Tb, Yb inverse opals. The upconversion luminescence of the Tb3+ ions is suppressed in the inverse opal compared with the luminescence of that of the reference sample.Highlights► Upconversion emission from Tb3+ was observed in the SiO2: Tb, Yb inverse opal. ► UC emission of Tb3+ was modulated by controlling the structure of inverse opal. ► UC emission of Tb3+ was depressed in the inverse opal.

Influence of competition between excited-state absorption and spontaneous emission from intermediate excited state on upconversion emission was investigated firstly in photonic crystals. The result clearly shows that upconversion emission can be modulated by the photonic crystal. When upconversion emission band from intermediate excited state overlaps with the photonic band gap, short wavelength unconversion emission from upper state is obviously enhanced due to an inhibition of spontaneous emission from the intermediate excited state in the photonic crystal. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also new optical devices in upconversion displays and short wavelength upconversion lasers.Highlights► Upconversion (UC) inverse opal (LaPO4:Yb, Tb) photonic crystals were prepared. ► An enhancement of excitation state absorption was realized in the inverse opal. ► UC emission suppression from intermediate excited state was detected in inverse opal. ► An enhancement of UC emission from upper excited state was obtained.

Polymerization crystalline colloidal arrays (PCCA) were fabricated by light polymerization method. Microstructures of polymerization crystalline colloidal arrays were observed by SEM. The results show that the microspheres in the PCCA form into a face-centered cubic structure with (111) plane parallel to the surface of the quartz cell. In addition, the influence of photonic band gap on photoluminescence of dyes was also investigated in the PCCA. Suppression of the emission was observed if the photonic band gap overlapped with the dyes emission band in the PCCA. Suppression of the emission was attributed to the photon trapping of the Bragg reflection in the PCCA.

The upconversion (UC) luminescence and color tunable properties of Tb3+ ions were investigated by steady spectral under 980 LD excitation in the Ca0.15Zr0.85O1.85:Yb,Tb inverse opals fabricated by the self-assembly technique in combination with a sol-gel method. The inhibition of UC emission was inspected if the Tb3+ UC emission band was in the regions of the photonic bandgap, while enhancement of the UC emission occurred if the UC emission band located at the edge of the bandgap. Color modification of the UC emission was successfully obtained by the suppression or enhancement effect of the photonic band gap on the UC emission.

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.

A new method for enhancing the upconversion (UC) emission of rare-earth doped nanoparticles is reported, in which Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles are deposited on to the surface of photonic crystal (PC) films. The UC emission of the Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles on the PC surface was notably enhanced when the UC emission bands of the Yb3+/Er3+ or Yb3+/Tm3+ co-doped NaYF4 nanoparticles were within the range of the photonic band gap of the PCs, indicating that the PCs were efficient and selective reflection mirrors. The results show that PCs may have potential applications in UC optoelectronics and lighting devices.