Teng-Ming Chen

Sr3B2O6:Ce3+,Eu2+: A potential single-phased white-emitting borate phosphor for ultraviolet light-emitting diodes

The Ce3+∕Eu2+ coactivated Sr3B2O6 phosphors exhibit varied hues from blue through white and eventually to yellow-orange by resonance-type energy transfer from Ce3+ to Eu2+ and tuning the relative proportion of Ce3+∕Eu2+ properly. The authors have demonstrated that electric dipole-dipole interaction dominates the energy transfer mechanism in Sr3B2O6:Ce3+,Eu2+ phosphor, and the critical distance of energy transfer has been estimated to be about 30A by both spectral overlap and concentration quenching methods. They have also shown that under the excitation of UV radiation, white light is generated by coupling 434 and 574nm emission bands attributed to Ce3+ and Eu2+ radiations, respectively.

White-light generation and energy transfer in SrZn2(PO4)2:Eu, Mn phosphor for ultraviolet light-emitting diodes

The SrZn2(PO4)2:Eu2+,Mn2+ phosphor shows two emission bands under ultraviolet radiation; the one observed at 416nm is attributed to Eu2+ occupying the Sr2+ sites and the other asymmetric band deconvoluted into two peaks was found to center at 538 and 613nm, which originate from Mn2+ occupying two different Zn2+ sites. The energy transfer from Eu2+ to Mn2+ has been demonstrated to be a resonant type via a dipole-quadrupole mechanism. By utilizing the principle of energy transfer and appropriate tuning of activator contents, we have demonstrated that SrZn2(PO4)2:Eu2+,Mn2+ is potentially useful as an ultraviolet-convertible phosphor for white-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.

(Ca,Mg,Sr)9Y(PO4)7:Eu2+,Mn2+: Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer

Two series of single-composition (Ca,Mg,Sr)9Y(PO4)7:Eu2+ and (Ca0.5Sr0.5)9Y(PO4)7:Eu2+,Mn2+ phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn2+ concentration-dependent photoluminescence properties, we found that co-doping with Mn2+ would lead to a change in Eu2+/Eu3+ ratio. Moreover, an energy transfer from Eu2+ to Mn2+ occurs because of the spectral overlap between the emission band of Eu2+ and the excitation band of Mn2+. The resonance-type energy transfer via a dipole–quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca0.5Sr0.5)9Y(PO4)7:0.007Eu2+,0.02Mn2+ and blue-emitting (Ca0.5Mg0.5)9Y(PO4)7:0.007Eu2+ phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca0.5Sr0.5)9Y(PO4)7:0.007Eu2+,0.02Mn2+ and (Ca0.5Mg0.5)9Y(PO4)7:0.007Eu2+ is potentially useful for white n-UV light-emitting diodes (LEDs).

Ca(2)PO(4)Cl : Eu(2+): an intense near-ultraviolet converting blue phosphor for white light-emitting diodes

A blue phosphor Ca2PO4Cl:Eu2+ was synthesized by solid state reaction and evaluated as a candidate for white LEDs. The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm, 149% under 400 nm, and 247% under 420 nm, as high as that of BaMgAl10O17:Eu2+. Furthermore, Ca2PO4Cl:Eu2+ reveals high quantum efficiency and excellent thermal stability. By utilizing a mixture of blue-emitting Ca2PO4Cl:Eu2+, green-emitting (Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ as light converters, an intense white GaN-based n-UV-LED (400 nm) was fabricated to exhibit an excellent color-rendering index Ra of 93.4 at a correlated color temperature of 4590 K. Based on the results, we are currently evaluating the potential application of Ca2PO4Cl:Eu2+ as a blue-emitting near-UV convertible phosphor.

White light generation under violet-blue excitation from tunable green-to-red emitting Ca2MgSi2O7 : Eu, Mn through energy transfer

Yellowish green-to-orange red emission can be generated by energy transfer from Eu2+ to Mn2+ in the Ca2MgSi2O7 host matrix. Eu2+-doped Ca2MgSi2O7 shows a broad green emission band centering at 528nm and Mn2+-doped Ca2MgSi2O7 exhibits a red emission at around 602nm. The authors have demonstrated that the mechanism of energy transfer from Eu2+ to Mn2+ in Ca2MgSi2O7:Eu,Mn phosphor is a resonant type via a dipole-quadrupole mechanism. They have also shown that the white light with varied hue, depending on contents of Mn2+, is generated by combination of predesigned emission wavelength-tunable Ca2MgSi2O7:Eu,Mn phosphors and violet-blue light source.

Ce3+∕Eu2+ codoped Ba2ZnS3: A blue radiation-converting phosphor for white light-emitting diodes

The Ce3+∕Eu2+ codoped Ba2ZnS3 phosphor shows intense blue absorption and tunable green-to-red emission. The energy transfer from Ce3+ to Eu2+ in this phosphor has been demonstrated to be a resonant type via an electric dipole-dipole mechanism. The Ba2ZnS3:Ce3+,Eu2+ phosphor would be the great potential application as a blue radiation-converting phosphor for white light-emitting diodes.

Eu2+-Activated Sr8ZnSc(PO4)(7): A Novel Near-Ultraviolet Converting Yellow-Emitting Phosphor for White Light-Emitting Diodes

The crystal structure of Eu(2+)-activated Sr(8)ZnSc(PO(4))(7):Eu(2+) phosphor was refined and determined from XRD profiles by the Rietveld refinement method using a synchrotron light source. This phosphor crystallizes in the monoclinic structure with the I2/a space group. The SZSP:xEu(2+) phosphors showed a broad yellow emission band centered at 511 and 571 nm depending on the concentration of Eu(2+), and the composition-optimized concentration of Eu(2+) in the Sr(8)ZnSc(PO(4))(7):Eu(2+) phosphor was determined to be 2 mol %. The estimated crystal-field splitting and CIE chromaticity coordinates of Sr(8)ZnSc(PO(4))(7):xEu(2+) (x = 0.001-0.05 mol) were 20181-20983 cm(-1) and (0.3835, 0.5074) to (0.4221, 0.5012), respectively, and the emission band showed a redshift from 547 to 571 nm with increasing Eu(2+) concentration. The nonradiative transitions between the Eu(2+) ions in the Sr(8)ZnSc(PO(4))(7) host were attributable to dipole-dipole interactions, and the critical distance was approximately 19.8 Å. The combination of a 400 nm NUV chip with a blend of Sr(8)ZnSc(PO(4))(7):0.02Eu(2+) and BAM:Eu(2+) phosphors (light converters) gave high color rendering indices between 79.38 and 92.88, correlated color temperatures between 4325 and 7937 K, and tuned CIE chromaticity coordinates in the range (0.381, 0.435) to (0.294, 0.310), respectively, depending on the SZSP:0.02Eu(2+)/BAM:Eu(2+) weight ratio. These results suggest that the Sr(8)ZnSc(PO(4))(7):0.02Eu(2+)/BAM:Eu(2+) phosphor blend has potential applications in white NUV LEDs.

High color rendering white light-emitting-diode illuminator using the red-emitting Eu(2+)-activated CaZnOS phosphors excited by blue LED.

A red phosphor CaZnOS:Eu(2+) was synthesized by solid state reaction and has been evaluated as a candidate for white LEDs. For this material, the XRD, PL, PL excitation (PLE) and diffuse reflection spectra have also been investigated. CaZnOS:Eu(2+) reveals a broad absorption band and good color purity. By utilizing a mixture of red-emitting CaZnOS:Eu(2+), green-emitting (Ba,Sr)(2)SiO(4):Eu(2+) and yellow-emitting Y(3)Al(5)O(12):Ce(3+) as light converters, an intense white InGaN-based blue-LED (~460 nm) was fabricated to exhibit a high color-rendering index Ra of 85 at a correlated color temperature of 4870 K. Based on the results, we are currently evaluating the potential application of CaZnOS:Eu(2+) as a red-emitting blue-chip convertible phosphor.

BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes

In this paper, a cyan-emitting phosphor BaZrSi3O9:Eu2+ was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 380–420 nm region, and the emission intensity of the optimized BaZrSi3O9:Eu2+ was found to be 90% and 198% of that of the commercial BaMgAl10O17:Eu2+ (BAM:Eu2+) under excitation at 405 nm and 420 nm, respectively. Upon excitation at 405 nm, the quantum efficiency of the optimized BaZrSi3O9:Eu2+ is 83% of that of BAM:Eu2+. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaZrSi3O9:Eu2+ with a green-emitting (Ba,Sr)2SiO4:Eu2+ and a red-emitting CaAlSiN3:Eu2+ on a near-ultraviolet (405 nm) LED chip, driven by a 350 mA forward bias current, intense warm white light with a color rendering index of 90 has been produced.