The reaction temperature was controlled to investigate the formation process of S-doped CDs (CDs-S). Different low-molecule-weight organics were used as precursors, it reveals that the N and/or S atoms containing in the precursors are related to the formation and luminescence mechanism.

In this work, a transition metal doped Ce3+-based borate CeZn1−x(B5O10):Mn2+ was synthesized by utilizing conventional solid-state reaction method. The lattice structure and particularly the luminescence properties of the synthesized phosphors were carefully studied. By analyzing the results, it is revealed that Mn2+ only occupies Zn sites, and it only contributes the light emitting peaked at 615 nm under the excitation of 371 nm. While the emitting peak at 437 nm under the same excitation is verified to be caused by the 5d-4f (2F5/2 and 2F7/2) transitions of Ce3+-based. Furthermore, by conducting a comprehensive investigation on overlap of emission, excitation spectra and variation of fluorescence decay lifetimes, we make it clear that the energy transfer from Ce3+ to Mn2+ is virtually via a resonance-type mechanism. Last but not the least, we can realize color-tunable light emitting by adjusting the concentration of Mn2+ in our proposed phosphor and using excitation of ultraviolet (UV) light. In addition, close to white light can be realized when doping the Mn2+ ions to a certain extent.

A novel single-phase color-tunable phosphor, Eu2+-activated Li4SrCa(Si2O4N8/3):Eu2+ (LSCSN:Eu2+), was synthesized via the conventional solid-state reaction method. The crystal structure of LSCSN has been determined by Rietveld refinement on X-ray powder diffraction data, and it was found that LSCSN crystallizes in an orthorhombic unit cell with the space group Pbcm(57). Under the excitation of UV light, the phosphor shows two main emission bands peaking at 430 nm and 578 nm, which have been confirmed to correspond to Eu2+ occupying the ten-coordination Sr sites and six-coordination Ca sites, respectively. Subsequently, the energy transfer between different Eu2+ emission centers was verified by the overlap of the emission and excitation spectra and the variation of fluorescence decay lifetimes. Meanwhile, when the excitation was changed to 375 nm light, it was found that the color hue can be tuned from blue to yellow, and even white if the Eu2+ ion concentration was increased to some extent. The thermal stability of the phosphor has been also investigated, which performs well with a high value of stability along with its integrated emission intensity remaining as 90.9% at 150 °C of that measured at room temperature. Furthermore, a warm white LED has been fabricated with a LSCSN:0.03Eu2+ phosphor and a 375 nm LED chip, and when the applied current is set to be 80 mA, the white LED was found to have a color rendering index (Ra) of 82.5 at the CIE coordinates of (0.3568, 0.3111) and correlated color temperature of 3318 K. The outstanding luminescence properties suggested that our prepared samples have potential application in w-LEDs.

Carbon dots, the new member of carbon materials, have attracted much attention for their alluring optical properties showing intense blue and green emission. Herein, carbon dots were synthesized by the hydrothermal method. Eu3+ β-diketonate complexes with characteristic emission were selected as the lanthanide resource. Silica-based ionogels were prepared by a sol–gel route, the ionic liquids in the ionogels were extracted with acetonitrile, and nano-sized pores among the ionogels were obtained. The carbon dots and Eu3+ complexes were homogeneously entrapped in the ionogels without any devitrification by doping the ionic liquid solution in the silica network of the ionogels. The obtained Eu3+-doped ionogel-functionalized carbon dot monoliths are transparent and uniform with promoted mechanical properties and stability. The carbon dots were confined in the nano-sized pores among the ionogels, resulting in there being a certain distance between the carbon dots, as well as preventing them from aggregating, which contributed to a high photoluminescence. The monoliths emit bright white photoluminescence under UV excitation after various studies of the proportion of carbon dots and Eu3+ complexes. Eu3+-doped ionogel-functionalized carbon dot monoliths provide new potential for applications of carbon nanoparticles in optoelectronic devices.

A novel Ca2.89Mg0.11(PO4)2:Eu2+ single-phase white light-emitting phosphor was synthesized by solid-state reactions and its crystal structure and luminescence properties were investigated. The Ca2.89Mg0.11(PO4)2:Eu2+ phosphor was found to have a trigonal structure with a space group R3c. The broad excitation spectra, ranging from 250 to 400 nm, matched well with near-UV LED chips. The much wider emission bands from 365 to 675 nm included more than one peak. Furthermore, the intensity of the peak at about 413 nm gradually decreases, while those in longer wavelengths gradually increase with the increase in Eu2+ concentration. Correspondingly, the emission hue varied from purplish-white to white and eventually to yellowish-white under 365 nm excitation. These results suggested that the Ca2.89Mg0.11(PO4)2:Eu2+ phosphor was a color tone tuning single-phase white light-emitting phosphor. Therefore, Ca2.89Mg0.11(PO4)2:Eu2+ is expected to be a promising candidate for white LEDs.

A series of emission-tunable NaSr(4−x−y)Bax(BO3)3:yEu2+ phosphors have been prepared by a conventional solid-state reaction method. The structures of NaSr(4−x−y)Bax(BO3)3:yEu2+ have been investigated by Rietveld refinement of the X-ray diffraction (XRD) patterns. The results indicated that the as-prepared samples showed the same crystal structure of NaSr4(BO3)3 with a cubic unit cell and space group of Iad. With the increase of Ba2+ concentration, the Sr2+ sites were replaced by Ba2+ completely and the lattice parameter of the unit cell increased from a = b = c = 15.0710 Å to 15.7266 Å. Both emission spectra and decay curves of NaSr3.98(BO3)3:0.02Eu2+ and NaBa3.98(BO3)3:0.02Eu2+ showed the existence of two different Eu2+ emission centers named Eu1 and Eu2. Eu2 was six-coordinated and Eu1 was eight-coordinated of oxygen. With the increase of Eu2+ concentration in the NaSr3−yBa(BO3)3:yEu2+ sample, the emission intensity increased and reached a maximum at y = 0.02. Then the concentration quenching phenomenon emerged due to the electric dipole–dipole interaction. Upon the cation substitutions (Sr2+ for Ba2+) in the NaSr(4−x−y)Bax(BO3)3:yEu2+ host, the emission peaks of Eu2+ blue-shifted from 609 nm to 544 nm and the thermal stability decreased, which was ascribed to the change of the covalency and the crystal field strength that the 5d orbital of the Eu2+ ion experiences. The CIE chromaticity coordinates of the obtained phosphors can be continuously tuned from orange-red (0.4795, 0.4070) to yellow-green (0.3432, 0.4665) by adjusting the Ba2+ concentration. The results demonstrate that the emission-tunable NaSr(4−x−y)Bax(BO3)3:yEu2+ phosphors have a potential application for white light emitting diodes (w-LEDs).

Mn2+/Eu2+ co-activated Sr3Si6O3N8 phosphor was synthesized by conventional solid state reaction. Sr3Si6O3N8:Eu2+, Mn2+ green-emitting phosphor could be effectively excited by UV–visible light from 300 nm to 500 nm, which matched well with the emission of UV and blue LED chips. The luminescence intensity of Sr3Si6O3N8:Eu2+ could be efficiently enhanced by co-doping with Mn2+ ions. The energy transfer mechanism between Eu2+ and Mn2+ in Sr3Si6O3N8:Eu2+, Mn2+ phosphors is dominated by electric multipole effect interaction.

An emission-tunable, Eu2+-activated, Ba2Ca(PO4)2:Eu2+ phosphor was synthesized by a conventional solid-state reaction. X-ray powder diffraction (XRD) and FT-IR spectroscopic analysis confirmed the phase formation. Electron paramagnetic resonance (EPR) analysis indicated there are three different crystallographic Ba2+ sites, namely, Ba(1), Ba(2) and Ba(3), occupied by the Eu2+ ions. The excitation and emission spectra, concentration dependence of the emission intensity and decay curves of the phosphor were investigated. The results showed that with increasing Eu2+ concentration, the emission peak wavelength redshifted from 457 to 500 nm, and the color hue can be tuned from a greenish blue to a yellowish green. A white LED was fabricated using a near ultraviolet (n-UV) 410 nm chip pumped with a blend of phosphors consisting of greenish blue-emitting Ba1.97Ca(PO4)2:0.03Eu2+ and red-emitting Ca3.97(PO4)2O:0.07Eu2+. When the applied current was 350 mA, the white LED had Commission International de l'Eclairage color coordinates of (0.3249, 0.3421) at a white light (correlated color temperature = 6020 K) and an excellent color rendering index of 93.

Transparent Ni2+-doped SiO2-Al2O3-Ga2O3-Li2O (LGAS) glass–ceramics embedding lithium aluminate spinel nanocrystals was prepared. After heat treatment, LiAl5O8 crystallite was precipitated in the glasses, and its size was about 3 nm. It was confirmed from the absorption spectra that the ligand environment of Ni2+ ions changed from the trigonal bi-pyramid fivefold sites in the as-made glass to the octahedral sites in the glass–ceramics. Upon excitation at 980 nm, broadband infrared luminescence centered at around 1250 nm with full width at half maximum (FWHM) more than 250 nm was observed originating from the 3T2(3F) → 3A2(3F) transition of Ni2+ in octahedral sites. The broadband near-infrared (NIR) emission from Ni2+-doped glass–ceramics can be as host materials for broadband optical amplifier.Research Highlights► Transparent Ni2+-doped SiO2-Al2O3-Ga2O3-Li2O glass-ceramics embedding lithium aluminate spinel nanocrystals was prepared, after heart-treatment, LiAl5O8 crystallite was precipitated in the glasses, and its size was about 3 nm. ► Upon excitation at 980 nm, Broadband infrared luminescence centered at around 1250 nm with full width at half maximum more than 250 nm was observed.

A transparent Er3+–Tm3+–Yb3+ tri-doped oxyfluoride glass ceramics containing LiYF4 nanocrystals were prepared. Under 980 nm laser diode (LD) pumping, intensive red, green and blue upconversion (UC) was obtained. The blue, green, and red UC radiations correspond to the transitions 1G4→3H6 of Tm3+, 2H11/2/4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3+ ions, respectively. This is similar to that in Tm3+–Yb3+ and/or Er3+–Yb3+ co-doped glass ceramics. However, the blue UC radiations of the Er3+–Yb3+ co-doped glass ceramics is two-photon process due to cooperative energy transfer. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.

A novel tunable red to yellow emitting phosphor, (Ca, Ba)4(PO4)2O:Eu2+ is reported that displays a broad emission from 500 to 800 nm, and its emitting color can be adjusted from red to yellow by changing Ba2+ doping concentration. X-ray powder diffraction (XRD) analysis confirmed the phase formation. Excitation and emission spectra, and concentration dependence of emission intensity of the phosphor were investigated. The results showed that the emission peak wavelength take blue-shifted from 640 to 545 nm and the color hue can be tuned from red to yellow with increasing Ba2+ concentration. When single-phase (Ca3.85Ba0.10)(PO4)2O:0.05Eu2+ phosphor is pumped by a blue InGaN light-emitting diode, we obtain white light with color rending index (Ra) between 84.0 and 90.6 and color temperatures between 4000 and 5500 K, which suggests that this material is competitive as a color conversion material for solid state lighting.

An emission-tunable, Eu2+-activated, Ba2Ca(PO4)2:Eu2+ phosphor was synthesized by a conventional solid-state reaction. X-ray powder diffraction (XRD) and FT-IR spectroscopic analysis confirmed the phase formation. Electron paramagnetic resonance (EPR) analysis indicated there are three different crystallographic Ba2+ sites, namely, Ba(1), Ba(2) and Ba(3), occupied by the Eu2+ ions. The excitation and emission spectra, concentration dependence of the emission intensity and decay curves of the phosphor were investigated. The results showed that with increasing Eu2+ concentration, the emission peak wavelength redshifted from 457 to 500 nm, and the color hue can be tuned from a greenish blue to a yellowish green. A white LED was fabricated using a near ultraviolet (n-UV) 410 nm chip pumped with a blend of phosphors consisting of greenish blue-emitting Ba1.97Ca(PO4)2:0.03Eu2+ and red-emitting Ca3.97(PO4)2O:0.07Eu2+. When the applied current was 350 mA, the white LED had Commission International de l'Eclairage color coordinates of (0.3249, 0.3421) at a white light (correlated color temperature = 6020 K) and an excellent color rendering index of 93.