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Abstract: Upconversion luminescence of rare‐earth ions doped nanoparticles can be enhanced by the localized surface plasmon resonance (LSPR) of noble metals nanoparticles, which was extensively investigated. The semiconductor nanomaterials such as the WO2.72 exhibited the tunable LSPR, which provide the possibility for the luminescence enhancement of upconversion nanoparticles. In this work, the urchin‐like WO2.72 was successfully prepared by solvothermal method, exhibiting the LSPR in the near infrared region. The influence of LSPR of WO2.72 on the upconversion luminescence of NaYF4:Yb3+,Er3+ nanoparticles was investigated firstly. The 525, 542, and 660 nm upconversion luminescence of NaYF4: Yb3+,Er3+ nanoparticles was increased by the 10, 8, and 12 factors, respectively, which was from the enhanced excitation field induced by the WO2.72 film. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we present a facile preparation approach of Au nanoparticles embedded LaPO4:Eu3+ inverse opal photonic crystals. In the typical preparation process, the transparent LaPO4:Eu3+ sol including HAuCI4 was infiltrated into the opal templates. After the sintering, the 10‐20 nm Au nanoparticles were formed in the interior of nano‐sized wall of LaPO4:Eu3+ inverse opal and the Au nanoparticles embedded LaPO4:Eu3+ inverse opals were obtained. The luminescence of Au nanoparticles embedded LaPO4:Eu3+ inverse opal was investigated. The emission peaks located at the 593 (5D0→7F1), 618 (5D0→7F2) and 698 nm (5D0→7F4) from Eu3+ ions were observed. The 593, 618, and 698 nm emissions of Au nanoparticles embedded LaPO4:Eu3+ inverse opals were enhanced in contrast to these of LaPO4:Eu3+ inverse opal without the Au nanoparticles, which is from the excitation field enhancement caused by the localized surface plasmon resonance of Au nanoparticles. [ABSTRACT FROM AUTHOR]

A special core/shell/shell structured NaYF4/NaYF4:Yb3+,Er3+/NaYF4 (CSS) nanocrystal was designed to ensure each luminescence center in the emitting shell had the same surroundings. The nanocrystal includes a support core NaYF4 nanoparticle in the center coated by a thin emitting shell NaYF4:Yb3+,Er3+ and another NaYF4 shell with adjustable thickness as the outer shielding shell. The green upconversion fluorescence intensity Ig(d) of the CSS nanoparticles shows an exponential relationship with the thickness d of the shielding shell. When d decreased to 0, Ig(0) was ~356 times smaller than Ig(∞) due to the drastic fluorescence quenching of the rare earth luminescence centers by the surroundings. Our experimental results indicate that ~90% of the severe effect of the surroundings can be eliminated by coating with a ~4 nm-thick NaYF4 shielding shell. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we reported a series of halosilicate photoluminescence (PL) materials, which have the chemical composition Ba5SiO4(F x Cl6−x ):0.05Eu2+ (x =0, 1, 3, 4, 6). It is found that, under 365-nm UV light, Ba5SiO4Cl6:Eu2+ phosphor exhibits strong blue light with peak wavelength at 442 nm. By adding small amount of F− to the host lattice for the substitution of Cl−, the emission wavelength of the Ba5SiO4(F, Cl)6:Eu2+ phosphor changes to 503 nm, corresponding to the green light. The possible luminescence mechanism in this phosphor system was also discussed. [Copyright &y& Elsevier]

CaF2:Yb3+,Er3+ upconversion (UC) luminescence nanoparticles have been synthesized using mesoporous silica (SBA-15) as a hard template. The samples were characterized by x-ray diffraction, Fourier transform infrared spectra, field-emission scanning electron microscopy, transmission electron microscopy, and UC emission spectra, respectively. Highly crystalline cubic phase CaF2:Yb3+,Er3+ nanoparticles are uniformly distributed with an average diameter of about 40-50 nm, and the formation process is also demonstrated. The UC fluorescence has been realized in the as-prepared CaF2:Yb3+,Er3+ nanoparticles on 980-nm excitation. The UC emission transitions for 4F9/2-4I15/2 (red), 2H11/2-4I15/2 (green), 4S3/2-4I15/2 (green), and 2H9/2-4I15/2 (violet) in the Yb3+/Er3+ codoped CaF2 nanoparticles depending on pumping power and temperature have been discussed. The UC mechanism, especially the origin on the temperature-dependent UC emission intensities ratio between 2H11/2 and 4S3/2 levels, have been proposed. [ABSTRACT FROM AUTHOR]

Abstract The upconversion (UC) nanoparticles (NPs) based sensor exhibits the potential application for the detection of dyes, heavy metal ions and DNA et al. However, the application of upconversion NPs based sensor was limited due to its low UC luminescence intensity. In the present work, the SiO 2 opal photonic crystals were prepared by the self-assembly technology. After infiltration of SiO 2 opal by the transparent chloroauric acid solution and the following sintering at the high temperature, the Au NPs/opal hybrids were prepared. The Au NPs/opal hybrids result in the enhancement of excited electric field, which can be served as the template of UC emission enhancement of NaYF 4 :Yb3+, Er3+ NPs exited at the 980 nm. The corresponding maximum UC emission enhancement was about 17-fold. The detection of Rhodamine B was realized by monitoring the changing of green UC intensity of NaYF 4 :Yb3+, Er3+ NPs. In comparison with pure NaYF 4 :Yb3+, Er3+ NPs, the sensor sensitivity of NaYF 4 :Yb3+, Er3+ NPs deposited on the Au NPs/opal hybrid was increased by about the 35-factors, which exhibits a low detection limit of 164 μM and a high sensitivity of 1.15 μM−1. The present work demonstrated that this solid sensor exhibits potential applications in heavy metal ions and DNA et al. Graphical abstract Image 1 Highlights • The Au nanoparticles/opal photonic crystal hybrid was prepared by sintering method. • Upconversion emission enhancement of NaYF 4 nanoparticles has been largely improved. • The detection of Rhodamine B by NaYF 4 :Yb3+, Er3+ nanoparticles was realized. • The sensor sensitivity of NaYF 4 on the Au nanoparticles/opal hybrid was increased. [ABSTRACT FROM AUTHOR]

Metal nanoparticles preparation in the interior of nanoscale skeleton of inverse opals made up of crystallized matrix is more difficult than the preparation of pure inverse opals. In the present work, the Ag or Au nanoparticles embedded YbPO 4 :Er 3+ inverse opals were prepared by a simple approach, which involved the infiltration of opal template by using the transparent YbPO 4 :Er 3+ sol including silver nitrate or chloroauric acid and the sintering at high temperature. The 20–30 nm Au or 5–10 nm Ag nanoparticles were formed in the interior of nanoscale skeleton in the YbPO 4 :Er 3+ inverse opals, and the Ag or Au nanoparticles embedded YbPO 4 :Er 3+ inverse opals were prepared. The influence of Ag or Au nanoparticles on the upconversion photoluminescence of YbPO 4 :Er 3+ inverse opal was studied, and the upconversion luminescence enhancement induced by the Ag or Au nanoparticles was observed. The mechanisms of upconversion luminescence enhancement of YbPO 4 :Er 3+ inverse opals induced by Ag or Au nanoparticles were discussed. The enhancement of upconversion luminescence induced by Ag nanoparticles was attributed to the enhancement of the excitation field, and the enhancement of upconversion emission induced by Au nanoparticles was related to the increasing of the radiation decay rate of Er 3+ . [ABSTRACT FROM AUTHOR]

Optical thermometry via near-infrared (NIR) emitting luminescent nanoparticles has attracted a great deal of attention during the last few years. In particular, nanothermometers operating in the biological windows are being strongly demanded for biomedical applications. In this sense, Tm3+ emissions centered around 800 and 1800 nm were explored here for ratiometric thermometry. And a luminescent thermometer based on NaYbF 4 /NaYF 4 : Tm3+-Yb3+/NaYF 4 core/shell/shell-structured nanoparticles is designed. Excited by 980 nm laser, saturated emissions from Tm3+: 3H 4 →3H 6 (~800 nm: first biological window NIR-I) and Tm3+: 3F 4 →3H 6 (~1800 nm: third biological window NIR-III) transitions are readily obtained owing to the efficient upconversion processes in the core/multishells nanoparticles, finally resulting in the same dependence of NIR emissions on the pumping power. Different thermal response between 800 and 1800 nm emissions of Tm3+ ions enables optical thermometry via ratiometric method. In the physiological temperature range, the relative sensitivity S r and absolute sensitivity S a achieved here are about 0.33% K−1 and 3.9% K−1, respectively, with a temperature uncertainty of 0.75 K. These results illustrate that the nanothermometer developed in this work would be promising candidate for optical temperature measurement in bio-fields. • The potential application of Tm3+ NIR emissions in ratio thermometry is verified. • The sensing emissions are located in the NIR-I and NIR-III region. • Core/multishells nanoparticles were designed to ensure reliable sensing. [ABSTRACT FROM AUTHOR]