Phosphors For near-UV Light-emitting Diodes Research Articles

Color Tunability of Blue Phosphors by Changing Cations for Near-UV InGaN-Based Light-Emitting Diode

The serials of blue phosphors, CaAl2Si2O8: Eu2+ doped with different content Sr2+ and Mg2+ ions, were prepared by solid-state reaction at high temperature. And their structure and photo-luminescent properties were investigated. In Ca0.96-ySryAl2Si2O8: 0.04Eu2+ (y = 0.10, 0.30, 0.50, 0.70, 0.90) system, for y ≦ 0.03, all the compositions crystallize in triclinic structure of CaAl2Si2O8, and on further increase of y, the system undergoes a compositionally induced phase transition from triclinic to monoclinic structure. For Ca0.96-yMgyAl2Si2O8: 0.04Eu2+ (y = 0.10, 0.30, 0.50, 0.70, 0.90) system, for z ≦ 0.03, all the compositions are of triclinic structure of CaAl2Si2O8. With the further increase of z, other phase appears. The emission spectra of these phosphors show blue shift with the introduction of Sr2+ ions, and red shift with Mg2+ ions. The reason may be due to the difference ionic radii of Mg2+, Ca2+, Sr2+. These phosphors show excellent blue emission and broad excitation band in near-UV (ultraviolet) range. They may be potential phosphors for near-UV light-emitting diodes (LEDs).

Spectral and surface investigations of Ca2V2O7:Eu3+ nanophosphors prepared by citrate-gel combustion method: a potential red-emitting phosphor for near-UV light-emitting diodes

In the present work, red-emitting Ca2V2O7:xEu3+ (x = 0.5–6.0 mol%) nanophosphors, in the form of powders, were synthesized by the citrate-gel combustion method using metal nitrates as precursors and citric acid as fuel. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy were used to study the structure, morphology and spectral properties of the samples. The chemical compositions and electronic states of the powders were analyzed with X-ray photoelectron spectroscopy. The average crystallite sizes estimated using the XRD data were found to be in the range of 30–45 nm, and were cross verified by TEM. The lattice parameters determined by the POWD program were approximated as a = 7.242 A, b = 6.674 A, c = 6.932 A and V = 291.24 A3, respectively. Under UV (395 nm) (PL) and electron (CL) excitation, the nanophosphors show characteristic emission from the Eu3+ ion (5D0 → 7Fj, j = 1–5) with the main peaks at 612 and 616 nm. The maximum emission intensity was recorded from the sample with an Eu3+ concentration of 4 mol% and a critical energy distance of 19.084 A between the donor and the acceptor. Above this concentration, there was a reduction in the intensity due to dipole–dipole induced concentration quenching effects. The potential applications of this phosphor as a high color-purity phosphor in light-emitting diodes are evaluated.

Photoluminescence properties of novel red-emitting NaSrBO3:Eu3+ phosphor for near-UV light-emitting diodes

A series of NaSrBO3:xEu3+ and NaSr1−2xBO3:xEu3+, xM+ (M=Li, Na, K) phosphors were synthesized by the solid state reaction. The crystal structure, photoluminescence properties and concentration quenching of NaSrBO3:Eu3+ phosphors were systematically investigated. The excitation spectra indicate that the phosphors can be efficiently excited by 394nm, which is matched well with the emission wavelength of near-UV LED chip. All the samples show the characteristic red emission of Eu3+ ions (5D0→7FJ, J=0, 1, 2, 3 and 4). The maximum intensity of luminescence is observed at the Eu3+ concentration around x=0.11. The concentration quenching of Eu3+ in NaSrBO3:Eu3+ phosphor can be mainly attributed to quadrupole–quadrupole interaction. The relative emission intensities of Eu3+ (5D0→7F2) in NaSrBO3:Eu3+ phosphors with Li+, Na+ or K+ introduced as charge compensator are significantly enhanced, and the phosphors added with K+ ions show the strongest emission. The emission intensities of NaSr1−2xBO3:xEu3+, xM+ (M=Li, Na, K) are about 1.47, 1.64 and 2.08 times than that of commercial red phosphor Y2O2S:Eu3+. These results indicate that NaSr1−2xBO3:xEu3+, xM+ (M=Li, Na, K) phosphors exhibit potential applications in the field of near-UV LED as an efficient red-emitting phosphors.

Luminescent and thermal properties of a new green emitting Ca 6Sr 4(Si 2O 7) 3Cl 2:Eu 2+ phosphor for near-UV light-emitting diodes

A novel green emitting phosphor, Eu 2+-activated Ca 6Sr 4(Si 2O 7) 3Cl 2, was synthesized using the solid-state reaction and its temperature-dependent luminescence characteristic was reported for the first time. Crystallographic site-occupations of Eu 2+ ions in this host were assigned and two distinguishable Sr 2+ sites were confirmed. As the temperature increases, the emission lines of Ca 6Sr 3.99(Si 2O 7) 3Cl 2:0.01Eu 2+ show an anomalous blue-shift along with the broadening bandwidth and decreasing emission intensity, which is ascribed in terms of the phonon-assisted back tunneling from the excited state of low-energy emission band to the high-energy emission band in the configuration coordinate diagram. Further, the luminescence quenching temperature, the activation energy for thermal quenching (Δ E), and the chromaticity coordinates were also investigated. In view of its preferable excitation spectrum profile, intense green emission peaking at 511 nm, and high thermal luminescence stability, the as-prepared phosphor is expected to find applications as a new green emitting phosphor for near-UV light emitting diodes.

High efficiency and high color purity blue-emitting NaSrBO3:Ce3+ phosphor for near-UV light-emitting diodes

A highly intense blue-emitting phosphor NaSrBO3:Ce3+, peaking at 400 nm was synthesized by a solid state reaction. The crystal structure, luminescence properties and quantum efficiency of NaSrBO3:Ce3+ phosphors, as well as their thermal quenching capabilities and the fabrication of a 370 nm UV-chip and R/G/B phosphors were investigated for the first time. The composition-optimized NaSrBO3:1%Ce3+ exhibited high external quantum efficiency of 89% of the blue-emitting, commercial compound, BaMgAl10O17:Eu2+ (BAM:Eu2+). The color purity of as-synthesized NaSrBO3:1%Ce3+ phosphor is much better than that of BAM:Eu2+. By using a GaN-based UV-LED (370 nm) and a mixture of blue-emitting NaSrBO3:Ce3+, green-emitting (Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors as light converters, we constructed an intense white light emitting diode. The LED device exhibited an excellent color-rendering index Ra of 93.13 at a correlated color temperature of 5763 K with CIE coordinates of (0.324,0.337) and a maximum lumen efficacy of 26.2 lm W−1. Based on the results, we are currently evaluating the potential application of NaSrBO3:Ce3+ as a blue-emitting UV convertible phosphor.

High-Color-Purity Red Phosphor for Near-UV Light-Emitting Diodes

A series of red phosphors, doped with boron oxide, were prepared by the conventional solid-state reaction. Their excitation spectra and emission spectra were measured at room temperature. With the introduction of boron oxide, the red-emission intensity of the phosphors under excitation are strengthened and have high color purity. In the fabricated phosphor light-emitting diodes, a bright red light can be observed by the naked eye.

Thermally stable luminescence of blue LiSrPO4:Eu2+ phosphor for near-UV light-emitting diodes

Blue phosphor, LiSrPO4:Eu2+, was prepared by solid-state reaction method under a weak reductive atmosphere and investigated by means of photoluminescence, concentration quenching process, and temperature dependence of luminescence. These results show that LiSrPO4:Eu2+ can be efficiently excited by the UV-visible light of 250–440 nm and exhibits bright blue emission. Furthermore, Eu2+-doped LiSrPO4 phosphor shows high thermally stable luminescence comparable to commercial phosphor BaMgAl10O17:Eu2+ (BAM). Two bright blue LEDs were fabricated by incorporating an InGaN-based near-UV chip with the obtained phosphor LiSrPO4:Eu2+ and BAM, respectively. Their luminescence properties were compared based on different forward-bias currents. All the characteristics suggest that LiSrPO4:Eu2+ is a good blue phosphor candidate for creating white light in phosphor-conversion white LEDs.

Photoluminescent Properties of (La,Eu,Sm)[sub 2]W[sub 3]O[sub 12] Red Phosphor for Near-UV-LED-Based Solid-State Lighting

Luminescent properties of Sm 3+ -co-doped (La,Eu) 2 W 3 O 12 under near-UV light excitation have been investigated. L 0.5 Eu 1.5 W 3 O 12 shows efficient red emission at 616 nm and is about 1.7 times higher than Y 2 O 2 S:Eu 3+ in photoluminescence (PL) peak intensity under 395 nm light excitation. Meanwhile, 0.1 mol Sm 3+ -co-doped La 0.5 Eu 1.5 W 3 O 12 is over 5 times higher than Y 2 O 2 S:Eu 3+ in PL peak intensity under 405 nm light excitation. These results imply that Sm 3+ -co-doped (La,Eu) 2 W 3 O 12 is a candidate of red phosphors for near-UV light-emitting diodes (LEDs), though the Sm 3+ co-doping causes an increase in thermal quenching of PL.