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Graphical abstract Highlights • Yb3+/Er3+/Eu3+ ions doped NaGdF 4 phosphors have been prepared by l -arginine assisted-hydrothermal method. • Dual-mode (up- and down-conversion) luminescence was achieved by Er3+, Eu3+ and Yb3+ doping. • Tunable color can be achieved by adjusting the contents of Eu3+ ions and excitation wavelength. • Unique optical and magnetic properties made the phosphors widely applied. Abstract Rare earth ions doped luminescence nanomaterials have broad applications ranging from television tubes to biological imaging. A series of Yb3+/Er3+/Eu3+ ions doped NaGdF 4 dual-mode (up- and down-conversion) luminescence phosphors have been prepared by l -arginine assisted-hydrothermal method. The results show that the synthesized samples are all pure β -NaGdF 4 with one dimensional micron structure. Changing the excitation wavelengths and Eu3+ ion concentrations, multiple (yellowish green, yellow, orange) emissions are obtained. Moreover, the energy transfer, luminescence mechanism and paramagnetic properties of the samples have been discussed in this paper. [ABSTRACT FROM AUTHOR]

An ultrafast route at room temperature has been developed for the first time to synthesize lanthanide ion (Yb3+/Er3+)-activated K0.3Bi0.7F2.4 fluorescent nanoparticles and hold the potential to be applied in luminescent temperature sensors. In addition, the crystal structure and morphology of the K0.3Bi0.7F2.4 nanoparticles prepared at different reaction conditions were studied in detail for the first time, including the reaction time and different mole ratios of Bi source and NH4F. Moreover, Yb3+/Er3+ doped in the K0.3Bi0.7F2.4 matrix using a luminescent thermometer based on the fluorescence intensity ratio technology was also investigated. Additionally, K0.3Bi0.7F2.4:Yb3+/Er3+ revealed excellent up-conversion luminescence performance, and the up-conversion mechanisms of samples are affirmed according to the up-conversion emission intensity as a function of the pump power density. Simultaneously, the optical thermometric performance of the samples was investigated in the temperature range of 323–523 K to indagate the temperature sensor performance. Significantly, the maximum sensor sensitivity of the studied nanoparticles were 0.0058 K−1 (Sa) at 523 K and 1.08 K−1 (Sr) at 323 K, which indicates that K0.3Bi0.7F2.4:20%Yb3+/2%Er3+ fluorescent nanoparticles can be exploited as a promising luminescent thermometer. [ABSTRACT FROM AUTHOR]

As a promising red component used in white light-emitting diodes (WLEDs), Mn4+ activated fluoride red phosphor has drawn tremendous attention due to its excellent luminescence properties. However, in order to synthesize these phosphors, the hypertoxic HF which will cause safety problems has to be used. In this work, a class of KZnF 3 :Mn4+ phosphors were synthesized by using low toxicity (HCl + NH 4 F) to substitute for HF at room temperature. The structure, morphology and element composition have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometers (EDS) in detail, respectively. The optical properties of KZnF 3 :Mn4+ were evaluated and we found that under blue light excitation, KZnF 3 :Mn4+ as expected exhibits a sharp narrow-band red emission near 636 nm. In addition, the synthesis parameters, including the molar ratios of (HCl + NH 4 F) to Zn(NO 3) 2 ·6H 2 O and reaction time on the luminescent properties of KZnF 3 :Mn4+ samples have been systematically discussed. Furthermore, the concentration quenching mechanism was also analyzed. Finally, it is assembled by YAG:Ce3+, KZnF 3 :Mn4+ and blue LED chip to achieve a WLED with a lower CCT (4974 K), higher CRI (Ra = 82.1) and a luminous efficiency of 120.33 lm/W. All of these results manifest that the KZnF 3 :Mn4+ phosphors prepared by green route would be a satisfactory material to ameliorate the performance of WLEDs. Red phosphors KZnF 3 :Mn4+ with cube morphology have been synthesized by using innoxious NH 4 F and HCl to substitute for hypertoxic HF at room temperature. Image 1 • KZnF 3 :Mn4+ red phosphors were synthesized by green route. • Concentration quenching mechanism was systematically discussed. • The KZnF 3 :Mn4+ red phosphors as expected exhibit a sharp narrow-band red emission. • The KZnF 3 :Mn4+ can be used as a red component to improve the performance of WLEDs. [ABSTRACT FROM AUTHOR]

Lanthanide-doped core-shell upconversion particles with tunable emission bands and intensities in response to external stimuli provide opportunities for multicolor barcoding, optical imaging, and temperature sensing applications. Here, we provide a universal template that can be used as a basic medium for color control and temperature sensing. In a representative nanostructure, i.e., NaYF 4 :Yb/Er@NaYF 4 :Yb/Tm, two excitation-emission spectra-orthogonal luminescence groups with naked-eye observable emission colors (cyan or yellow-green) were obtained by switching the excitation wavelength (980 and 1550 nm). Furthermore, the temperature-responsive optical performance of the nanostructure was investigated, and enhanced temperature sensitivities S a (0.2339 K−1) and S r (2.5286% K−1) were achieved based on 3F 2,3 /4S 3/2 non-thermally coupled energy levels (NTCLs). The photophysical properties of the nanostructure show great potential for anticounterfeiting and non-contact temperature sensing applications. ● Multifunctionality in simple core-shell microrods were developed. ● Two orthogonal luminescence groups with naked-eye certifiable emission colors were obtained in simple core-shell microrods. ● A real-time naked-eye recognizable color change of anti-counterfeiting pattern based on samples. ● The core-shell microrods show superior temperature sensitivity based on NTCLs for temperature sensing application. [ABSTRACT FROM AUTHOR]

• Doping transition-metal ions into the lattice of lanthanide doped materials aids in luminescence enhancement. • d-d electronic transitions of transition metals can stimulate the excited state properties of the lanthanide ions. • MoO 6 groups have a high rate of absorption in UV/NUV regions. • Mo-O charge transfer transition can enhance the luminescent properties of the co-doped lanthanide ions. • Adjusting Mo6+ dopage concentration codoped Dy3+/Eu3+ can emit white light out of the host. [Display omitted] In the present study, we successfully prepared single-host CaZrO 3 codoped Dy3+/Eu3+/Mo6+ for white light emission by employing solid state reaction method. Molybdenum was introduced into the lattice to enhance luminescence intensity of the phosphor materials. The luminescence properties of all the prepared samples were investigated under UV-lamp. The XRD results confirmed the formation of orthorhombic phase CaZrO 3. The SEM photographs realized that the prepared phosphor materials have a tendency to form agglomerates. Similarly, the EDS test was carried out to confirm the absence of any extraneous impurities. Mo6+ was incorporated into Dy3+ and Eu3+ singly doped, and also in Dy3+/Eu3+ codoped CaZrO 3. Furthermore, we also studied the energy transfer between Mo6+ → Dy3+ and Mo6+ → Eu3+ in detail. The increasing dopant concentration of Mo6+ (Mo = 0.1, 0.5, 0.8, 1.0, 2.0) mol% under 350 nm excitation source, the CIE color coordinates shift towards the vicinity of white light, which makes this material prominent for the fabrication of white light emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]

Mn4+ activated fluoride red phosphors, Na 2 GeF 6 :Mn4+, with controllable morphology and size, were successfully synthesized through simple coprecipitation method. Using the hollow Na 2 GeF 6 :Mn4+ particles, we successfully fabricated two-dimensional red-emitting nanofiber film via electrospinning technology. The phase purity, morphology and composition of the samples were confirmed via X-ray powder diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-ray spectrometer (EDS), respectively. Different surfactants were introduced into the experimental process, which successfully controlled the sample morphology. The broad excitation band from 300 nm to 550 nm matches well with commercial blue light emitting diodes, and narrow band emission red light can be observed in the range of 575–675 nm because of spin-forbidden 2E g - 4A 2g energy level transition of Mn4+ ion. The effect of doping concentration on luminescence and the mechanism of concentration quenching were discussed. On the basis of the experimental excitation (PLE) and emission (PL) spectra, the crystal field strength of the Mn4+ occupation environment was estimated and the nephelauxetic effect was researched for the Mn4+ ions in the Na 2 GeF 6 host. Temperature-dependent properties of Na 2 GeF 6 :Mn4+ particles and nanofiber film were systematically analysed. Moreover, the Na 2 GeF 6 :Mn4+ particles and nanofiber film can significantly change the performance of white light-emitting diodes (WLEDs), the nanofiber film is a more appropriate candidate than Na 2 GeF 6 :Mn4+ particle for warm WLED applications. Image 1 • Na 2 GeF 6 :Mn4+ red phosphor with controlled morphology and size were synthesized. • Crystal field parameters and nephelauxetic effect were systematically studied. • Using Na 2 GeF 6 :Mn4+, two-dimensional red-emitting nanofiber film were obtained. • Using Na 2 GeF 6 :Mn4+ nanofiber film, a high-performance warm WLED were obtained. [ABSTRACT FROM AUTHOR]