Panlai Li

A novel, warm, white light-emitting phosphor Ca2PO4Cl:Eu2+, Mn2+ for white LEDs

A series of single-phase phosphors, Ca2PO4Cl:Eu2+, Mn2+, have been successfully synthesized by a solid-state method and their photoluminescence properties have been investigated. Ca2PO4Cl:Eu2+, Mn2+ can be excited at wavelengths between 250 and 450 nm, which is within the range of the ultraviolet light-emitting diode (LED). As a result of fine tuning the emission composition of Eu2+ and Mn2+ ions, warm white light can be realized by combining the emission in a single host lattice under excitation by ultraviolet light. Efficient resonant energy transfer from Eu2+ to Mn2+ ions has been demonstrated to be a dipole–quadrupole mechanism in Ca2PO4Cl, and the energy transfer efficiency increases with increasing Mn2+ concentration, confirmed by luminescence spectra and fluorescence decay times. The energy transfer efficiency and critical distance have also been calculated. A warm, white LED has been fabricated using the single-phase white-emitting phosphor, Ca2PO4Cl:0.07Eu2+, 0.2Mn2+, pumped by a 400 nm LED chip. Our results give CIE chromaticity coordinates for the white LEDs as (0.3102, 0.3096), and a correlated color temperature of 4296 K. Ca2PO4Cl:Eu2+, Mn2+ is therefore able to serve as a potential, warm, white emitting material for white LEDs.

Luminescence and energy transfer of Eu2+/Tb3+/Eu3+ in LiBaBO3 phosphors with tunable-color emission

A series of LiBaBO3:RE (RE = Eu2+/Tb3+/Eu3+) phosphors have been synthesized using the high-temperature solid-state reaction method. The X-ray diffraction (XRD), emission spectra, excitation spectra, decay lifetimes, and diffuse reflection spectra were utilized to characterize the phosphors. The as-prepared samples have been characterized via XRD measurement and showed that Eu2+/Tb3+/Eu3+ can be efficiently doped into the host. The obtained phosphors can emit different colors of light when doping with different activators. The energy transfer from Tb3+ to Eu3+ occurs in LiBaBO3:0.03Eu3+,yTb3+ prepared in the air. While an abnormal reduction phenomenon was reported when Eu and Tb ions were co-doped in LiBaBO3 and prepared in an inferior reductive atmosphere, which showed tunable-color from blue to red based on energy transfer of Eu2+ → Tb3+ → Eu3+ ions. And the energy transfer not only can occur between Eu2+ and Tb3+ ions, but also between Tb3+ and Eu3+ ions. All these results reveal that Tb3+ can play the role of storing the energy for Eu3+, and LiBaBO3 may be a potential candidate phosphor for LEDs.

Crystal structure, luminescence properties, energy transfer and thermal properties of a novel color-tunable, white light-emitting phosphor Ca9−x−yCe(PO4)7:xEu2+,yMn2+

A series of Ca9-x-yCe(PO4)7:xEu2+,yMn2+ phosphors were synthesized by a high-temperature solid-state reaction method. The as-prepared samples were characterized by XRD and EDX measurements, which showed that Eu2+ and Mn2+ could be efficiently doped into the host. Ce3+ acts concurrently as activator and sensitizer in Ca9Ce(PO4)7, and the energy transfer mechanisms between Ce3+/Eu2+ and Ce3+/Mn2+ in Ca9Ce(PO4)7 were validated and proven to be a resonant type via dipole-quadrupole and dipole-dipole interactions, respectively. Besides, there is also energy transfer from Eu2+ to Mn2+ ions. The host, Ca9Ce(PO4)7, emits blue-white light and Ca9Ce(PO4)7:xEu2+,yMn2+ phosphors emit blue-green through white to orange-red light under near-ultraviolet radiation as a result of tuning the ratio of Eu2+/Mn2+. Ca9Ce(PO4)7:0.04Eu2+,0.08Mn2+ emits white light with CIE coordinates (0.333, 0.310), a CCT of 5446 K, and a high CRI of 81. The energy transfer efficiency between Ce3+ and Mn2+ increases significantly with temperature. These results reveal that Ca9Ce(PO4)7:Eu2+,Mn2+ may be a potential candidate for white light-emitting phosphors.

Tunable blue-green emitting and energy transfer of a Eu2+/Tb3+ codoped Sr3La(PO4)3 phosphor for near-UV white LEDs

A series of Eu2+ and Tb3+ doped Sr3La(PO4)3 phosphors have been synthesized via the high-temperature solid-state reaction method. X-ray diffraction (XRD) patterns, luminescence spectra including temperature-dependent luminescence spectra, and fluorescence decay lifetimes have been used to characterize the as-prepared samples. Under ultraviolet excitation, Sr3La(PO4)3:Eu2+ shows a strong blue emission around 418 nm and a shoulder centered at 500 nm, which is based on the substitution of two kinds of Sr2+ sites by Eu2+ ions (Eu1 and Eu2). Sr3La(PO4)3:Tb3+ shows characteristic emission lines of Tb3+ under 376 nm excitation. For Sr3La(PO4)3:Eu2+,Tb3+ phosphor, similar excitation spectra monitored at 418, 500 and 545 nm have been observed, which illustrates the possibility of energy transfer from Eu2+ to Tb3+ ions. Compared with the Tb3+ singly doped phosphor, the codoped phosphors have more intense absorption in the n-UV range and stronger emission of the Tb3+ ions, which are attributed to the effective energy transfer from the Eu2+ to Tb3+ ions. The variations in the emission spectra, emission color and decay lifetimes further demonstrate the existence of energy transfer from Eu2+ to Tb3+ ions under ultraviolet excitation. For Eu1 and Eu2, the energy transfer mechanism has been confirmed to be quadrupole–quadrupole and dipole–quadrupole interaction, respectively. The results can be validated via the agreement of critical distances obtained from the concentration quenching (21.62 A). These results show that the phosphors may possess potential application in ultraviolet-based white light-emitting diodes.

Luminescence and energy transfer of 432 nm blue LED radiation-converting phosphor Ca4Y6O(SiO4)6:Eu2+, Mn2+ for warm white LEDs

A series of Ca4Y6O(SiO4)6:Eu2+, Mn2+ phosphors are synthesized by a solid state method. Ca4Y6O(SiO4)6:Eu2+, Mn2+ can be excited at wavelength ranging from 250 to 500 nm, which is well matched with ultraviolet-visible light emitting diode. Under 432 nm excitation, Ca4Y6O(SiO4)6:Eu2+, Mn2+ can create warm white emission by energy transfer from Eu2+ to Mn2+. A warm white light emitting diode is fabricated by combining a 432 nm blue LED with a single phase warm white emitting phosphor Ca3.92Y6O(SiO4)6:0.05Eu2+, 0.03Mn2+, which has CIE chromaticity coordinates (0.336, 0.319), correlated color temperature (CCT) 4326 K and color rendering index (Ra) 86, respectively. The results indicate Ca4Y6O(SiO4)6:Eu2+, Mn2+ may serve as potential warm white emitting phosphor for blue LED based white LEDs.

Substituting Different Cations in Tuning of the Photoluminescence in Ba3Ce(PO4)3.

An attempt has been made to explore how the luminescence properties change when rare-earth elements are substituted for different cations in the host. We synthesized Eu(2+)-doped Ba3Ce(PO4)3 via a high-temperature solid-state reaction process, substituting for Ba(2+) and Ce(3+) ions and naming them Ba3Ce(1-x)(PO4)3:xEu(2+) and Ba(3-y)Ce(PO4)3:yEu(2+), respectively. The structure, X-ray diffraction with Rietveld refinements, reflectance spectra, and luminescence characterization of the phosphor are measured to explore the difference of substituting for different ions. In order to explain why all of the emission peaks containing the highest peak and the fitting values of Ba3Ce(1-x)(PO4)3:xEu(2+) are shorter than those of Ba(3-y)Ce(PO4)3:yEu(2+) (when x= y), we built a model by N, which represents the surrounding environment. This mechanism is predicted to be general to Eulytite-type orthophosphates and will be useful in tuning optical and other properties whose structural disorder influences the crystallization and is sensitive to local coordination environments. Substituting different cations in tuning of the red shift, widening of the full width at half-maxima (fwhm), and thermal quenching were also observed.

Research progress of Mn doped phosphors

In this review article, Mn applications have been divided into three parts. We provide an overview of recent progress in developing Mn4+ doped red phosphors for promising application in warm white light-emitting diodes. In addition, we summarize reports on Mn2+ co-doped Eu2+ or Ce3+ phosphors that can produce white light with outstanding color rendering index (CRI) and color coordinates via energy transfer processes, and report the application of Mn2+ in green to NIR phosphors.

Synthesis, color-tunable emission, thermal stability, luminescence and energy transfer of Sm3+ and Eu3+ single-doped M3Tb(BO3)3 (M = Sr and Ba) phosphors

A series of new tunable emission phosphors of Sm3+ and Eu3+ single-doped M3Tb(BO3)3 (M = Sr and Ba) phosphors were synthesized by the solid-state reaction. Crystallization behavior and structure, reflectance spectral properties, luminescence properties, energy transfer, lifetimes, temperature-dependent luminescence properties and CIE chromaticity coordinate of M3Tb(BO3)3:Ln3+ (M = Sr and Ba, Ln = Sm and Eu) were systematically investigated. M3Tb(BO3)3 (M = Sr and Ba) crystallizes in a rhombohedral cell with space group R by Rietveld structure refinement of the obtained phosphors with the standard data of Ba3Dy(BO3)3. Sr3Tb(BO3)3 and Ba3Tb(BO3)3 emit yellowish-green emission with the main peak around 555 and 550 nm, respectively, which originates from the 5D4 → 7F4 transition of Tb3+, and M3Tb(BO3)3:Ln3+ (Ln = Sm and Eu) phosphors show intense yellowish-green, yellow, orange and red emission with increasing Ln3+ concentration under 274 and 286 nm excitation. The orange-red/red emissions show peak maxima at 613 nm (Sr3Tb(BO3)3:Sm3+), 627 nm (Sr3Tb(BO3)3:Eu3+), 607 nm (Ba3Tb(BO3)3:Sm3+) and 625 nm (Ba3Tb(BO3)3:Eu3+), and are due to the efficient energy transfer of Tb3+–Sm3+ and Tb3+–Eu3+. The temperature-dependent luminescence properties of M3Tb(BO3)3:Ln3+ are characterised by good thermal stabilities up to 150 °C, up to 72.8%. However, due to the defect in the host of the Sr3Tb0.99(BO3)3:0.01Sm3+ phosphor, an amazing and interesting phenomenon can be observed that the emission intensity is enhanced constantly with increasing temperature.

Incorporating Ce3+ into a high efficiency phosphor Ca2PO4Cl:Eu2+ and its luminescent properties

A series of Ce3+, Eu2+ and Ce3+/Eu2+ doped Ca2PO4Cl phosphors are synthesized by a high temperature solid-state method. Not only is the emission intensity of Ca2PO4Cl:Eu2+ obviously enhanced by codoping Ce3+, but also the spectral profile of the excitation band is almost not influenced. The energy transfer from Ce3+ to Eu2+ in Ca2PO4Cl has been validated and proved to be a resonant type via a dipole–dipole interaction. Under the 400 nm radiation excitation, the luminescent intensity of Ca2PO4Cl:Ce3+, Eu2+ is found to be about 200% that of Ca2PO4Cl:Eu2+, and 300% that of BaMgAl10O17:Eu2+. The thermal quenching properties reveal that Ca2PO4Cl:Ce3+, Eu2+ has excellent characteristics. Therefore, Ca2PO4Cl:Ce3+, Eu2+ may have potential application as a blue-emitting phosphor for white LEDs.

Luminescence and energy transfer of tunable emission phosphor Ca2PO4Cl:Ce3+, Mn2+

A series of Ca2PO4Cl:Ce(3+), Mn(2+) phosphors are synthesized by a high temperature solid state reaction method, and their luminescent properties are investigated. Ca2PO4Cl:Ce(3+), Mn(2+) has an obvious absorption in the region of 300-350 nm, and energy transfer from Ce(3+) to Mn(2+) in Ca2PO4Cl has been validated, and proved to be a resonant type via a dipole-dipole interaction. Orange red emission intensity of Mn(2+) can be obviously enhanced via the efficient energy transfer from Ce(3+) to Mn(2+), and critical distance of energy transfer is also calculated by concentration quenching method, and about 14.1 Å. The results show that Ce(3+) ion may be an available sensitizer for Ca2PO4Cl:Mn(2+), and Ca2PO4Cl:Ce(3+), Mn(2+) may have potential application in white light emitting diodes.