Luminescence Properties of Eu[sup 2+]-Doped MAl[sub 2−x]Si[sub x]O[sub 4−x]N[sub x] (M=Ca, Sr, Ba) Conversion Phosphor for White LED Applications

Abstract

Undoped and Eu-doped MAl 2−x Si x O 4−x N x ͑M = Ca, Sr, Ba͒ were synthesized by a solid-state reaction method at 1300-1400°C under nitrogen-hydrogen atmosphere. The solubility of ͑SiN͒ + in MAl 2 O 4 was determined. Nitrogen can be incorporated into MAl 2 O 4 by replacement of ͑AlO͒ + by ͑SiN͒ + , whose amount of solubility depends on the M cation. The solubility of ͑SiN͒ + is very low in CaAl 2 O 4 and SrAl 2 O 4 lattices ͑x Ϸ 0.025 and 0.045, respectively͒, whereas a large amount of ͑SiN͒ + can be incorporated into BaAl 2 O 4 ͑x Ϸ 0.6͒. Incorporation of ͑SiN͒ + hardly modifies the luminescence properties of Eu 2+ -doped MAl 2 O 4 ͑M = Ca, Sr͒ because of limited solubility of ͑SiN͒ + , showing the blue and green emission at almost constant wavelength of 440 and 515 nm, respectively. Eu 2+ -doped BaAl 2−x Si x O 4−x N x exhibits a broad green emission band with a maximum in the range of 500-526 nm, depending on the concentration of ͑SiN͒ + and Eu 2+ . In addition, both excitation and emission bands of Eu 2+ show a significant red shift as nitrogen is incorporated. BaAl 2−x Si x O 4−x N x :Eu 2+ can be efficiently excited in the range of 390-440 nm radiation, which makes this material attractive as conversion phosphor for white light-emitting diode ͑LED͒ lighting applications. .As an important class of phosphors, Eu 2+ -doped MAl 2 O 4 ͑M = Ca, Sr, Ba͒, has been widely used as persistent luminescent materials because of their high efficiency, chemical stability, and long-lasting high-luminance afterglow characteristics. 1-3 These phosphors also have been proposed for plasma display panel ͑PDP͒ 4 and optoelectronic applications. 5 Under ultraviolet and cathode-ray excitation these phosphors show a strong blue ͑M = Ca͒, green ͑M = Sr͒, and blue-green ͑M = Ba͒ fluorescence.In MAl 2 O 4 ͑M = Ca, Sr, Ba͒, the three-dimensional framework is built-up by a motif of six rings formed by corner-sharing AlO 4 tetrahedra. The tetrahedral framework is isostructural, with the SiO 2 polymorph having the tridymite structure. 6-8 The various MAl 2 O 4 structures differ in the arrangement and number of crystallographic sites of the divalent cations within the channels formed by the AlO 4 rings. CaAl 2 O 4 has a monoclinic structure in space group P2 1 /n. In this structure there are three Ca sites: two of them are sixfold and the third is ninefold coordinated, with the oxygen atoms in a different channel. However, for the larger M cations, SrAl 2 O 4 and BaAl 2 O 4 crystallize in a monoclinic and a hexagonal system with the space group P2 1 and P6 3 , respectively. Both Sr and Ba ions occupy two crystallographic sites, which are located in the channels of the AlO 4 rings, each with ninefold coordination with the oxygen anions.Although extensive investigations have been done on Eu 2+ -doped alkaline earth aluminates MAl 2 O 4 ͑M = Ca, Sr, Ba͒, [9][10][11][12][13][14][15] in previous studies considerable attention has been paid to improve the performance of these phosphors by partial substitution of the M ion ͑for example, replacemen...

Transparent sunlight conversion film based on carboxymethyl cellulose and carbon dots

“…As we all know, sunlight conversion film is made up of two parts, including matrix and sunlight conversion agent, in which the latter plays a critical role in the performance of sunlight conversion properties. For sunlight conversion agent, many kinds of phosphors have been reported such as CaS:Cu + (Zhang, Li, Chen, Xiao, & Sun 2004), CaAl 2 O 4 :Eu 2+ (Li & Hintzen, 2006) and Ba 3 MgSi 2 O 8 :Eu 2+ (He et al, 2009). Compared with these doped phosphor, carbon dots (CDs), which consists a fascinating class of fluorescence-based nanoparticles, have emerged as important fluorescence materials because of their excellent photostability, chemical stability, high biocompatibility, and cost-effective preparation (Qu, Wang, Lu, Liu, & Wang, 2012).…”

Photoluminescence properties of Eu2+-activated sialon S-phase BaAlSi5O2N7

“…Recently, silicon nitride based compounds have been extensively studied as host lattices for phosphors, which exhibit unusual, interesting luminescence properties when activated by rare earth ions, such as M 2 Si 5 N 8 :Eu 2+ [1][2][3][4][5], M 2 Si 5 N 8 :Ce 3+ [6], MSi 2 O 2−␦ N 2+2/3␦ :Eu 2+ , Ce 3+ [7][8][9], CaSiN 2 :Eu 2+ [10], Ce 3+ [11], MgSiN 2 :Eu 2+ [12,13], MYSi 4 N 7 (M = Sr, Ba):Eu 2+ , Ce 3+ [14,15], MSi x Al 2−x O 4−x N x :Eu 2+ (M = Ca, Sr, Ba) [16], ␣-SiAlON:RE (RE = Eu 2+ , Ce 3+ , Yb 2+ , Tb 3+ , Pr 3+ , Sm 3+ ) [17][18][19][20][21][22][23], ␤-SiAlON:Eu 2+ [24], SrAlSi 5 O 2 N 7 :Eu 2+ [25], SrAl 2 SiO 3 N 2 :Eu 2+ [25], and CaAlSiN 3 :Eu 2+ [26]. Most importantly, these phosphors emit visible light efficiently under near-ultraviolet or blue light irradiation and have superior thermal and chemical stability to their oxide and sulfide counterparts, allowing them to be used as down-conversion luminescent materials for white light-emitting diodes (LEDs).…”

Enhanced luminescence properties of Sr3−xEuxAlO4−yNyF phosphors

“…Because the valence state of an activator ion depends on the coordination environment, the photoluminescent properties of phosphors can be controlled by modifying the covalency and polarizability of activator−ligand bonds in phosphors [11][12][13][14]. Moreover, the fluoride lattice provides a high coordination number for doped rare earth ions, and the high ionicity of the rare-earth-fluorine bond results in a wide band gap, low vibrational energies, and low probability of inter-configurational transitions [15].…”

“…Moreover, the fluoride lattice provides a high coordination number for doped rare earth ions, and the high ionicity of the rare-earth-fluorine bond results in a wide band gap, low vibrational energies, and low probability of inter-configurational transitions [15]. It has been previously reported that incorporating Si 4+ −N 3− into Ce 3+ -or Eu 2+ -doped phosphors will lead to a red shift in the 4f−5d emission owing to the lower electronegativity of N 3− compared to O 2− [11,12] Sample Characterization. The crystalline phases of each sample were identified by powder X-ray diffraction (XRD) measurements using a XD-3 diffractometer (PERSEE) with a Cu Kα radiation source (λ = 0.154 nm).…”