Spherical cerium-doped yttrium aluminum garnet (YAG:Ce3+) phosphor particles can achieve both higher packing densities and lower scattering of light, and thus make it possible to obtain excellent white-light-emitting diode performance. In this study, monodisperse YAG:Ce3+ microspheres have been synthesized through a fast epoxide-driven sol–gel route and subsequent heat treatment under a reducing atmosphere. The spherical morphology was mainly influenced by the phase separation and gelation process, which could be controlled by the ratio of water/ethanol. Pluronic F127 was introduced into the sol–gel system to control the size of the YAG:Ce3+ microspheres, which significantly increased the luminescence intensity of the YAG:Ce3+ microspheres. The luminescence quantum yield of the 6 mol% Ce3+ ion doped YAG microspheres was measured to be more than 90%, which was as high as that of commercial YAG:Ce3+ phosphors. This approach may be readily applied to prepare a broad range of rare earth doped microspheres, implying a new route for the preparation of LEDs phosphors with regular shape and high quantum yield.

An effective colloidal process involving the hot-injection method is developed to synthesize uniform single-crystalline Sb2Se3 nanorods in high yields. The photoconductive characteristics of the as-synthesized Sb2Se3 nanorods are investigated by developing a film-based photodetector and this device displays a remarkable response to visible light with an “ON/OFF” ratio as high as 50 (with an incident light density of 12.05 mW cm−2), short response/recovery times and long-term durability. To overcome the challenge of the intrinsic low electrical conductivity of Sb2Se3, hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure having a type-II band alignment are firstly prepared. The electric current of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film has been significantly increased both in the dark and under light illumination. The responsivity of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film is about 4.2 times as much as that of the photodetector based on the Sb2Se3 nanorod film. This improvement can be considered as an important step to promote Sb2Se3 based semiconductors for applications in high performance photodetectors.

Controlling excitation power is the most convenient approach to dynamically tuning upconversion that is essential for a variety of studies. However, this approach suffers from a significant constraint due to insensitive response of most upconversion systems to excitation power. Here we present a study of amplifying excitation power-sensitivity of upconversion in Ho3+ ions through the use of a NaYbF4 host. Mechanistic investigation reveals that the sensitive response of Ho3+ upconversion to excitation power stems from maximal use of the incident energy enabled by concentrated Yb3+ sensitizers. This allows us to sensitively tune the red-to-green emission intensity ratio from 0.37 to 5.19 by increasing the excitation power from 1.25 to 46.25 W cm–2, which represents a 5.6-fold amplification of the tunability (from 0.19 to 0.49) offered by Yb/Ho (19/1 mol %) codoped NaYF4. Our results highlight that the excitation-power sensitive upconversion emission can be exploited to experimentally visualize electromagnetic hotspots.

Correction for ‘Enhancement of charge photo-generation and transport via an internal network of Sb2Se3/Cu2GeSe3 heterojunctions’ by Xianghua Zhang et al., J. Mater. Chem. A, 2014, 2, 17099–17106.

An interpenetrating iodine-doped-Sb2Se3/Cu2GeSe3 heterojunction network has been fabricated by controlling the crystallization of a chalcogenide glass. These two crystals absorb strongly and widely the solar spectrum for efficient charge photo-generation, and the heterojunction formed by these two crystals greatly promotes the charge separation. More importantly, these free charge carriers can be efficiently transported through the conductive channels formed by the oriented Cu2GeSe3 nanoparticles aggregated between the Sb2Se3 rods. The photo-electrochemical measurement shows that this structure results in a photocurrent of 74 μA cm−2 and a photo-current/dark-current ratio over 12 times at a bias voltage of −0.6 V and under an illumination of 250 W cm−2. This photocurrent is at least 100 times higher than any of these two crystals individually.

In this study, hexagonal-phase NaY0.6–xCe0.1Gd0.3EuxF4 nanorods were synthesized via a mild solvothermal method. By modifying the Eu3+ dopant concentration, the crystal phase, morphology, and luminescent properties were well controlled. A broad excitation band centered at around 260 nm corresponding to the 2F5/2 → 4f-5d transition of Ce3+ was detected in the hosts containing Gd3+ ions by monitoring the Eu3+ emissions, indicating that an efficient Ce3+ → Eu3+ energy transfer occurred via the Gd3+ sublattice. Luminescence decay behaviors of the NaY0.6–xCe0.1Gd0.3EuxF4 nanorods were studied, and the energy transfer mechanism was discussed. An obvious rising edge on the luminescence decay curve of Eu3+ ions in the NaY0.6–xCe0.1Gd0.3EuxF4 nanorods was observed. The rising time is proposed to describe the energy migration time from Ce3+ to Eu3+ via the Gd3+ sublattice.

The preparation process and upconversion luminescence properties of the Yb3+ and Tm3+ co-doped glass ceramic containing SrF2 nanocrystals were investigated. In the glass ceramic, the SrF2 nanocrystals were embedded uniformly in the glass matrix. The Yb3+ and Tm3+ ions could be enriched into the precipitated SrF2 nanocrystalline phase, which provide much lower phonon energy than the glass matrix. The glass ceramic exhibited much stronger upconversion luminescence from ultraviolet to visible than the precursor glass. The upconversion luminescence mechanisms were mainly attributed to Yb3+–Yb3+ cooperative upconversion, Yb3+–Tm3+ energy transfer and Tm3+–Tm3+ cross relaxation.

A novel red SrMoO4:Sm3+,R+ (R+ = Li+, Na+, K+) phosphor was prepared by solid state reaction method. XRD results showed that 950 °C was a suitable sintered temperature for preparation of SrMoO4:Sm3+ phosphors. The emission spectra of the SrMoO4:Sm3+ phosphors consisted of some sharp emission peaks of Sm3+ ions centred at 562 nm, 601 nm, 646 nm, 703 nm, generating bright orange–red light. Luminescence concentration quenching could be observed when the doping concentration of Sm3+ ions was more than 2 mol%. The introduction of charge compensator R+ (R+ = Li+, Na+, K+) into the host efficiently enhanced the luminescence intensity of the SrMoO4:Sm3+ phosphors. The CIE chromaticity coordinates of the Sr0.96MoO4:0.02Sm3+,0.02Na+ phosphors was quite close to that of commercial red Sr2Si5N8:Eu2+ phosphors. These SrMoO4:Sm3+,R+ (R+ = Li+, Na+, K+) phosphors may be potentially used as red phosphors for white light-emitting diodes.

The Ce3+ and Tb3+ co-doped glasses and glass ceramics containing SrF2 nanocrystals were prepared by melt-quenching and subsequent heat treating and their luminescence properties were described. The formation of SrF2 nanocrystals in glass ceramics was confirmed by X-ray diffraction and transmission electron microscopy. The XRD patterns and photoluminescence spectra revealed that the Ce3+ ions and Tb3+ ions have been incorporated into SrF2 nanocrystals. The decay time of excited states has been used to reveal the energy transfer mechanism between Ce3+ and Tb3+. The emission intensity of Tb3+ ions in the glass ceramics was much stronger than that in the precursor glass, which could be ascribed to the more efficient energy transfer from Ce3+ to Tb3+ in the glass ceramics due to the enrichment of Ce3+ and Tb3+ ions and the shortening of the distance between Ce3+ and Tb3+ ions in the precipitated SrF2 nanocrystals. The glasses and glass ceramics could emit bright green light by adjusting concentration ratio of Ce3+ to Tb3+ and heat treatment temperature.

NaGdF4:Ce3+ and (Ce,Gd)F3 nanoparticles have been prepared by using a hydrothermal procedure. The hexagonal NaGdF4:Ce3+, cubic NaGdF4:Ce3+, or (Ce,Gd)F3 nanoparticles could be synthesized by controlling different molar ratio of reactants and synthesized temperatures. The emission spectra of the Ce3+ ions in the hexagonal NaGdF4:Ce3+ nanoparticles consisted of two broad bands at 360 nm and 524 nm. Only one broad emission band at 360 nm can be observed in the cubic NaGdF4:Ce3+ nanoparticles and the (Ce,Gd)F3 nanoparticles. The lifetimes of 360 nm emissions of Ce3+ ions varied from nanoseconds at 300 nm excitation to microseconds at 260 nm excitation due to an efficient energy transfer from the Gd3+ ions to Ce3+ ions.

Rare earth doped NaLa(WO4)2 nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The X-ray diffraction (XRD) pattern shows that the Eu3+-doped NaLa(WO4)2 nanoparticles with an average size of 10–30 nm can be obtained via hydrothermal treatment for different time at 180 °C. The luminescence intensity of Eu3+-doped NaLa(WO4)2 nanoparticles depended on the size of the nanoparticles. The bright upconversion luminescence of the 2 mol% Er3+ and 20 mol% Yb3+ codoped NaLa(WO4)2 nanoparticles under 980 nm excitation could also be observed. The Yb3+–Er3+ codoped NaLa(WO4)2 nanoparticles prepared by the hydrothermal treatment at 180 °C and then heated at 600 °C shows a 20 times stronger upconversion luminescence than those prepared by hydrothermal treatment at 180 °C or by hydrothermal treatment at 180 °C and then heated at 400 °C.

Reduction of Eu3+ → Eu2+ and luminescence of europium (Eu) ions in glass ceramics containing SrF2 nanocrystals have been investigated. The formation of SrF2 nanocrystals in glass ceramics was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Blue luminescence of the Eu2+ ions was observed in the Eu doped glass ceramics which were prepared by the heat treatment of the glass in air atmosphere. The double-exponential decay curves of 5D0 state of Eu3+ in the Eu doped glass ceramics indicated that there were two different surroundings of the Eu ions in the glass ceramics.

A Er3+ and Yb3+ co-doped transparent oxyfluoride glass ceramic containing BaF2 nanocrystals has been prepared. The formation of BaF2 nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er3+ and Yb3+ co-doped glass ceramic could be observed. Stark splitting of the Er3+ upconversion luminescence peaks in the glass ceramic indicated that Er3+ and Yb3+ had been incorporated into the BaF2 nanocrystals. Near infrared luminescence decay curves showed that the Er3+ and Yb3+ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.

Correction for ‘Enhancement of charge photo-generation and transport via an internal network of Sb2Se3/Cu2GeSe3 heterojunctions’ by Xianghua Zhang et al., J. Mater. Chem. A, 2014, 2, 17099–17106.

An interpenetrating iodine-doped-Sb2Se3/Cu2GeSe3 heterojunction network has been fabricated by controlling the crystallization of a chalcogenide glass. These two crystals absorb strongly and widely the solar spectrum for efficient charge photo-generation, and the heterojunction formed by these two crystals greatly promotes the charge separation. More importantly, these free charge carriers can be efficiently transported through the conductive channels formed by the oriented Cu2GeSe3 nanoparticles aggregated between the Sb2Se3 rods. The photo-electrochemical measurement shows that this structure results in a photocurrent of 74 μA cm−2 and a photo-current/dark-current ratio over 12 times at a bias voltage of −0.6 V and under an illumination of 250 W cm−2. This photocurrent is at least 100 times higher than any of these two crystals individually.