Blue, green, and yellow phosphors are obtained in the Sr1−xY0.98+xCe0.02Si4N7−xCx system (x=0→1). Decreases in thermal quenching barrier height with x result from a dominant neighboring‐cation effect, through which the replacement of Sr2+ by Y3+ reduces the covalency of CeN bonding. Green emission is observed from a cation‐segregated nanostructure of SrYSi4N7 and Y2Si4N6C domains in x=0.2–0.6 samples.

Novel promising blue MSiAl 2 O 3 N 2 :Ce 3+ (M = Sr, Ba) and green BaSiAl 2 O 3 N 2 :Eu 2+ oxynitride phosphors with broad band emission for white lightemitting diodes are obtained in this study. The detailed energy transfer mechanism from Ce 3+ to Eu 2+ in SrSiAl 2 O 3 N 2 is reported. Moreover, the unexpected red shift emission when the compositional variable x is increased from 0 to 0.92 in the Sr 0.92-x Ba x SiAl 2 O 3 N 2 :Ce 3+ 0.04 ,Eu 2+ 0.04 system is well investigated. The decrease in emission energy and the increase in thermal quenching barrier height of x are caused by a dominant chemical pressure compression effect on the activator sites, through which the replacement of Sr 2+ (occupied by activators) by larger Ba 2+ enhances the covalency of Sr−N/O bonding in spite of unit cell enlargement. The chemical pressure compression effect control for photoluminescence is verified by the ionic-radii equilibrium between 9-coordinate IX Sr 2+ and ( IX Ca 2+ , IX Ba 2+ ).

We have successfully prepared a novel nanoparticle solution of Sr2MgSi2O7: Eu 2+ , Dy 3+ with afterglow properties by means of laser ablation in liquid. This process also produced by-products of different kinds, depending on the liquid used. The amount of by-product and the size of the nanoparticles were controlled by the energy density of laser ablation. The amount of by-product was reduced by a decrease in the energy density, which also decreased the particle size of the nanoparticles. The PL spectrum of the nanoparticles was the same as that of the target materials used for laser ablation. The afterglow properties deteriorated with a decrease in particle size. We concluded that an increase in specific surface area caused by a decrease in particle size resulted in the decrease of luminescent intensity.

Red Ca0.99Al(1-4δ/3-x)Si(1+δ+x)N(3-x)C(x):Eu(2+)0.01 (δ = 0.345; x = 0-0.2) nitride phosphors exhibit a blue-shifted emission with increased eye sensitivity function and excellent thermal stability. The variations in the photoluminescence in the Ca0.99Al(1-4δ/3-x)Si(1+δ+x)N(3-x)C(x):Eu(2+)0.01 (δ = 0.345; x = 0-0.2) system are thoroughly investigated. The enhanced emission energy and the improved thermal stability with increasing x are dominated by the second-sphere shrinkage effect via the substitution of small Si(4+) for large Al(3+) with simultaneous charge compensation. Related proofs of the second-sphere shrinkage effect control for photoluminescence are confirmed via high-resolution neutron powder diffraction, EXAFS, and (29)Si solid-state NMR techniques.

Phosphor materials play a key role in white-light emitting diode (LED) devices based on gallium indium nitride (GaInN). [1][2][3][4][5] Phosphors for white LEDs should have good thermal stability and conversion efficiency and an excitation wavelength range in the UV to blue region (370-460 nm). [3,[6][7][8] The yellow-emitting phosphor (Y,Gd) 3 (Al,Ga) 5 O 12 :Ce 3+ is a well-known commercial example, but the lack of red emission results in cold white light and a low color-rendering index (CRI). [1,7,9,10] Nitride-based materials are more covalent than oxides, which improves thermal stability, and their greater crystal field splitting increases the red emission leading to warmer white light. [1,2,11,12] The chemistry of doped nitride phosphors is often complex and it may be difficult to understand how substitutions tune photoluminescence properties, as the local environment of activator ions may be quite different to the structural average. For example, local O/N ordering driven by the size mismatch between the Eu 2+ activator and the host cations was found to be an important effect in M 1.95 Eu 0.05 Si 5Àx Al x O 8Àx N x (M = Ca, Sr, Ba) phosphors. [12] Herein we demonstrate a new approach to controlling phosphor properties through segregation of activator cations on the nanoscale, as applied to Sr 1Àx Y 0.98+x Ce 0.02 Si 4 N 7Àx C x carbidonitridosilicate phosphors, and we show that overall trends evidence a significant neighboring-cation influence.Two structure types are encountered in the studied system. The SrYSi 4 N 7 (1147) type structure with hexagonal (space group P6 3 mc) symmetry contains a network of cornerlinked N(SiN 3 ) 4 structural units. [13][14][15][16] Sr and Y sites are coordinated by 12 and 6 nitrides, respectively. The related

The optical properties of afterglow nanoparticles were successfully improved by the addition of polyethylene glycol (PEG) to an afterglow colloidal solution. Afterglow nanoparticles-Sr 2 MgSi 2 O 7 : Eu 2+ , Dy 3+ -were prepared by laser ablation in liquid. The quantum yields and the decay curves were measured by a fluorescence spectrophotometer. An increase in the amount of PEG added to the solution increased the quantum yield of the nanoparticles and improved the afterglow property in the initial portion of the decay curve. However, the afterglow property did not change after a substantial amount of time had passed. The afterglow nanoparticles were capped with PEG molecules, and surface defects of the nanoparticles were passivated, which decreased the optical properties.

Yellow single crystals of aluminum silicon nitrides containing strontium and europium were prepared by heating starting mixtures of Sr3N2, Si3N4, AlN, and EuN at 2050°C and 0.85 MPa of N2 for 8 hours. Single‐crystal X‐ray diffraction revealed that prismatic crystals 20‐100 μm in size were Sr0.31Al0.62Si11.38N16:Eu (trigonal, a=7.7937(2) Å, c=5.6519(2) Å, space group P31c), which are isotypic with Sr‐α‐SiAlON, Srm/2Alm+nSi12−m−nN16−nOn, with m=0.62 and n=0. The Eu2+ content was approximately 1 at.% of Sr contained in the framework of corner‐sharing (Al/Si)N4 tetrahedra with an occupancy of 0.154(2). Block‐shaped crystals with a side length of 50‐300 μm were a new polytypoid of Sr‐α‐SiAlON, Sr2.97Eu0.03Al6Si24N40. Streak lines were observed in the direction of the c* axis in the X‐ray oscillation photographs, indicating stacking faults of the structure. The fundamental X‐ray reflections were indexed with a hexagonal cell (a=7.9489(3) Å, c=14.3941(6) Å). The structure was analyzed with a model of space group Ptrue6false¯ in which one of the six Al/Si sites was statistically split into two sites with occupancies of 0.673(5) and 0.227(5). The atomic arrangements in the layers of the structure were similar to those of Sr‐α‐SiAlON, but the stacking sequences of the layers were different. The peak wavelengths and full widths at half maximum of emission spectra measured for the single crystals of Sr0.31Al0.62Si11.38N16:Eu and Sr2.97Eu0.03Al6Si24N40 were 583 nm and 87 nm, and 584 nm and 91 nm, respectively, under 400 nm wavelength light excitation at room temperature.

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