⿢Synthesis of SrSi2O2N2: Eu2+ using 2-steps with four different preparation methods.⿢β-Sr2SiO4 phase has a significant effect on the crystallite size.⿢Luminescence of SrSi2O2N2: Eu2+ is affect by the proportion of β-Sr2SiO4 phase.⿢Synthesis method plays a big role to obtain high-efficiency SrSi2O2N2: Eu2+ phosphors.SrSi2O2N2: Eu2+ (SSON) phosphors were prepared using two-steps synthesis method with Sr2SiO4: Eu2+ (SSO) as a precursor. In the first step, coprecipitation (CO), Pechini sol-gel (PSG), sol-gel (SG), and solid-state reaction (SS) methods were performed, whereas the second step was used SS method. The effects of the α- and β-SSO phases in the first step on the luminescence intensity, crystallite size, and quantum efficiency of SSON in the second step are investigated. The photoluminescence results of SSON show an emission spectrum band between 460 and 640 nm with green emission peaks at 530 nm. The luminescence emission intensity of SSON phosphor was increased in the order of CO, PSG, SG, and SS methods. The results indicate that increasing of β-SSO phase in the first step using a specific preparation method is an important key to obtain high-efficiency SSON phosphors for their promising application in WLEDs.

In this research, Ca-α-SiAlON phosphors with compositions of Ca1−xEuxSi9Al3ON15 (x=2.5%, 5.0%, 7.5%, 10.0% and 15.0%) were synthesized by heterogeneous precipitation processing. The solid state reaction and nitridation reaction were completed at 1400–1500 °C for 12 h in a flow of N2–H2 (H2, 5 vol%). The phase of α-SiAlON was prepared at 1450 °C for 12 h. The phosphors showed strong and broad absorption in the range of 230–530 nm and a broad orange–yellow emission band ranging from 500 to 700 nm for peaking at 582–600 nm which were corresponding to the phosphor prepared by the conventional solid state reaction. The results indicate a concentration quenching effect at x≥7.5% and a systematic red-shift in emission wavelength as the heat-treatment temperature or the Eu2+ concentration increases. The quantum efficiency of the sample heat-treated at 1600 °C for 12 h, reached 70.56% (internal) and 45.7% (external) with the 450 nm excitation. The corresponding CCT (Correlated color temperature) range of white LED lamps consisting of a blue LED chip and the Ca-α-SiAlON phosphor can be ranging from 2000 to 2700 K.

Lu3−xAl5O12:xCe3+ (LuAG:Ce3+) green phosphors were synthesized by a two-step solid state reaction method. Morphology and optical properties of the phosphors were studied by adding various fluxes (BaF2, H3BO3, NH4Cl, NaF), as well as the concentration of different flux materials were optimized for maximum luminescence intensity. X-ray diffraction, scanning electron microscopy and photoluminescence spectra measurement were used to investigate crystal structure, particle morphologies and luminescence properties, respectively. The obtained phosphors with fluxes possessed better particle morphologies than that of the phosphors without fluxes. The particle size distribution and the luminescence intensity of the obtained phosphors were predominantly dependent on the type and concentration of flux materials. The results showed that the maximum luminescence intensities were found with the following order: BaF2 (3 wt%)>NaF (0.5 wt%)>NH4Cl (2 wt%)>H3BO3 (4 wt%)>no flux.

•Hydroxides of aluminum were firstly used as gelling agent to prepare LuAG: Ce3+ phosphors.•Both nano and micron scale products can be obtained and they are suitable for the fabrication of laser scintillators and white light emitting diodes, respectively.•Dispersion and crystallinity can be improved by using the two-step process.Ce3+-doped lutetium aluminum garnet (LuAG) phosphors have been successfully synthesized by a facile carbon-free sol–gel method without using any organic gelling agent. Phase transitions from gel to LuAG were well investigated by X-ray diffraction and thermal analysis. The results confirmed that a pure LuAG phase can form at around 920 °C by directly crystallizing from amorphous material. Particle size of the LuAG phosphor can be controlled by adjusting the heat treatment process; therefore, both nano and micron-scale products can be obtained and they are suitable for the fabrication of laser scintillators and white light emitting diodes, respectively. Agglomeration can be observed in the nano-sized phosphor. For the micron-sized LuAG, a two-step process was used to avoid hard agglomeration. Particles of the obtained micron-sized phosphor are uniform and well-dispersed. Luminescence properties of the phosphors were characterized. Relative intensity of the micron-sized product is comparable with commercial phosphor.

•Ce ions prefer to occupy Ca sites rather than Ba sites.•Dipole–dipole interaction is the concentration quenching mechanism of Ce3+ in BCS:Ce3+ phosphor.•Dipole–dipole mechanism contributes to the energy transfer between Ce3+ and Eu2+.•The phosphors could find potential applications in near UV light-emitting diode.Ce3+ doped and Ce3+–Eu2+ co-doped Ba1.3Ca0.7SiO4 phosphors are synthesized by the conventional solid state reaction method. The Ce3+ activated sample exhibits five excitation bands peaking at 240, 257, 280, 327 and 362 nm, which are attributed to the five energy levels due to 5d splitting, and has two intense blue emission bands peaking at 398 and 431 nm by two sites. It is discussed that Ce3+ substituted coordinated number 10 and 12 of Ca sites in Ba1.3Ca0.7SiO4. It was found that the emission intensity of Ba1.3Ca0.7−xSiO4:xCe3+ phosphors increases clearly with increasing of Ce3+ concentration and reaches a maximum at 1 mol%. The energy transfer between Ce3+ and Eu2+ ions is investigated with increasing Eu2+ ions at fixed Ce3+ concentration, the energy transfer is determined to be due to the dipole–dipole interaction mechanism.