Synthesizing pure phase Ba3Si6O9N4 by the conventional solid-state reaction method is challenging because of easily formed secondary phase Ba3Si6O12N2 showing similar crystal structure. In this work, an alternative low temperature synthesis method is presented, and a series of green to blue emitting (Ba, Sr)3Si6O9N4: Eu2+ phosphors were prepared by a mechanochemical activation route. Variations in photoluminescence properties and crystal structure, as induced by the change in phosphor composition, were investigated. Under ultraviolet-light excitation, Ba3Si6O9N4: Eu2+ phosphor exhibited a strong narrow green emission at 518 nm and simultaneously a weak emission at 405 nm, which are ascribed to different Eu/Ba sites in Ba3Si6O9N4 lattice proved by Density Functional Theory (DFT) calculations. A continuous green to blue emission in (Ba, Sr)3Si6O9N4: Eu2+ phosphors could be achieved by tuning the crystal structure and local coordination environment acting on Eu2+ with Sr/Ba substitution. More Sr/Ba substitution improved thermal quenching and resulted in a different characteristic of emission peak shift upon increasing the temperature.@en

To modify the luminescence properties of Ce³⁺-doped Y₃Al₅O₁₂ (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N₂ atmosphere. Luminescence of the carbon coated YAG:Ce³⁺ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce³⁺ is the highest when heated at 1650 °C, while a blue emission at 400-420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce³⁺-1500 °C, which disappear in C@YAG:Ce³⁺-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce³⁺ emission and the presence of the blue emission observed for C@YAG:Ce³⁺ -1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce³⁺ phosphors, which is related to a reaction between C and YAG:Ce³⁺ in N₂ atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N₂ atmosphere.

@en

Structural and optical properties of MGa2S4 (M = Mg, Zn, Ca, Sr, Ba) compounds have been compared, and the vacuum referred binding energy (VRBE) schemes were constructed for the lanthanide ions in the iso-structural compounds CaGa2S4 and SrGa2S4 employing literature data. The VRBE of an electron in the 5d excited state of Eu2+ was found at 0.75 and 0.97 eV below the bottom of the conduction band (CB) in CaGa2S4:Eu and SrGa2S4:Eu, respectively. Such differences explains the unexpected higher thermal quenching temperature reported for Eu2+-doped SrGa2S4 (T50% = ∼475 K) compared to Eu2+-doped CaGa2S4 (T50% = 400 K) The significantly lower VRBE at the CB-bottom in CaGa2S4 versus SrGa2S4 may be explained by the shorter Ga-S bond lengths in SrGa2S4.@en

The β-sialon:Eu2+ phosphor has superior luminescent properties as an excellent green down-conversion material for white light-emitting diodes. To take advantage of its high chromaticity and apply it to field emission displays (FEDs), the drawback of its electron insulation that impedes the electron transmission when excited by e-beam needs to be solved. In this work, a facile method was adopted to coat conductive In2O3 on the surface of β-sialon:Eu2+ phosphor, and the influence of In2O3 coating on the cathodoluminescent properties was investigated. The results show that the In2O3 coating contributes to charge elimination and significantly improves the cathodoluminescence (CL) of β-sialon:Eu2+. Under 19 kV/1.0 nA e-beam excitation, the In2O3 coated sample shows CL intensity about four times higher than that of the uncoated β-sialon:Eu2+. Moreover, no luminescence saturation occurs in coated β-sialon:Eu2+, indicating that the In2O3-coated β-sialon:Eu2+ would be a promising green emissive material for full-color FEDs.@en

The β-sialon:Eu2+ phosphor has superior luminescent properties as an excellent green down-conversion material for white light-emitting diodes. To take advantage of its high chromaticity and apply it to field emission displays (FEDs), the drawback of its electron insulation that impedes the electron transmission when excited by e-beam needs to be solved. In this work, a facile method was adopted to coat conductive In2O3 on the surface of β-sialon:Eu2+ phosphor, and the influence of In2O3 coating on the cathodoluminescent properties was investigated. The results show that the In2O3 coating contributes to charge elimination and significantly improves the cathodoluminescence (CL) of β-sialon:Eu2+. Under 19 kV/1.0 nA e-beam excitation, the In2O3 coated sample shows CL intensity about four times higher than that of the uncoated β-sialon:Eu2+. Moreover, no luminescence saturation occurs in coated β-sialon:Eu2+, indicating that the In2O3-coated β-sialon:Eu2+ would be a promising green emissive material for full-color FEDs.@en

The red-emitting Sr ₂ Si ₅ N ₈ :Eu ²⁺ phosphor with a superior quantum efficiency and suitable emission spectrum has been widely used as a promising down-conversion material in white light-emitting diodes. However, its thermal degradation under high temperature handicaps its large scale application, and therefore must be reduced. Here, we proposed to increase the thermal stability of Sr ₂ Si ₅ N ₈ :Eu ²⁺ by coating a nanometer-order Al ₂ O ₃ film on each phosphor particle using an atomic layer deposition approach in a fluidized bed reactor. The deposited Al ₂ O ₃ layer was quite uniform and conformal when using O ₃ as the oxidizer, and its thickness could be controlled by the dosage type, deposition temperature and cycle numbers, which largely affects the photoluminescence properties and thermal degradation of the title phosphor. Thermal gravimetric analysis results showed that the oxidation temperature of the coated phosphor increased from 700 to 850 °C, suggesting that the coating layer has the function of anti-oxidation. Meanwhile, the coated phosphor particle surface became hydrophobic. Consequently, the thermal degradation of phosphor powders in air at 200 °C was greatly reduced and the stability of the fabricated LEDs with coated powders was also improved. Prospectively, the proposed approach provides a new strategy to improve the thermal stability of other phosphors.

@en

The red-emitting Sr ₂ Si ₅ N ₈ :Eu ²⁺ phosphor with a superior quantum efficiency and suitable emission spectrum has been widely used as a promising down-conversion material in white light-emitting diodes. However, its thermal degradation under high temperature handicaps its large scale application, and therefore must be reduced. Here, we proposed to increase the thermal stability of Sr ₂ Si ₅ N ₈ :Eu ²⁺ by coating a nanometer-order Al ₂ O ₃ film on each phosphor particle using an atomic layer deposition approach in a fluidized bed reactor. The deposited Al ₂ O ₃ layer was quite uniform and conformal when using O ₃ as the oxidizer, and its thickness could be controlled by the dosage type, deposition temperature and cycle numbers, which largely affects the photoluminescence properties and thermal degradation of the title phosphor. Thermal gravimetric analysis results showed that the oxidation temperature of the coated phosphor increased from 700 to 850 °C, suggesting that the coating layer has the function of anti-oxidation. Meanwhile, the coated phosphor particle surface became hydrophobic. Consequently, the thermal degradation of phosphor powders in air at 200 °C was greatly reduced and the stability of the fabricated LEDs with coated powders was also improved. Prospectively, the proposed approach provides a new strategy to improve the thermal stability of other phosphors.

@en