Haikun Liu

A novel single-composition trichromatic white-emitting Sr3.5Y6.5O2(PO4)1.5(SiO4)4.5 : Ce3+/Tb3+/Mn2+ phosphor: synthesis, luminescent properties and applications for white LEDs

A series of single-composition trichromatic white-emitting Sr3.5Y6.5O2(PO4)1.5(SiO4)4.5 (SYPSO) : Ce3+, Tb3+, Mn2+ phosphors were investigated, and the crystal structures and luminescence properties, especially the energy transfer behavior, are discussed in detail. It was found that the SYPSO : Ce3+, Tb3+, Mn2+ phosphors can yield three major RGB emission bands in the visible spectral region: blue emission from the 5d–4f transitions of Ce3+, green emission from the 5D4–7FJ (J = 3, 4, 5, 6) transitions of Tb3+ and red emission from the 4T1(4G)–6A1(6S) transition of Mn2+ ions. The energy transfer process between Ce3+ and Tb3+ and between Ce3+ and Mn2+ have both been demonstrated to be a resonant type via a dipole–dipole mechanism, and the energy transfer (ET) efficiency, as well as the critical distance, have also been estimated. Based on the energy transfer, the emission colors of the obtained phosphors can be tuned from blue to green/red, and eventually to white emission by controlling the doping content of the Tb3+/Mn2+ ions. A white light emitting-diodes (w-LEDs) lamp was finally fabricated using the present phosphor (with the composition of SYPSO : 0.05Ce3+, 0.25Tb3+, 0.25Mn2+), which exhibited a high color rendering index (Ra) of 89.95 at a correlated color temperature of 6189 K and CIE coordinates of (0.320, 0.318). These results suggested that the present phosphor is a potential single-component white-light phosphor for n-UV-pumped w-LED.

Crystal structure and Temperature-Dependent Luminescence Characteristics of KMg4(PO4)3:Eu2+ phosphor for White Light-emitting diodes

The KMg4(PO4)3:Eu2+ phosphor was prepared by the conventional high temperature solid-state reaction. The crystal structure, luminescence and reflectance spectra, thermal stability, quantum efficiency and the application for N-UV LED were studied respectively. The phase formation and crystal structure of KMg4(PO4)3:Eu2+ were confirmed from the powder X-ray diffraction and the Rietveld refinement. The concentration quenching of Eu2+ in the KMg4(PO4)3 host was determined to be 1mol% and the quenching mechanism was certified to be the dipole–dipole interaction. The energy transfer critical distance of as-prepared phosphor was calculated to be about 35.84Å. Furthermore, the phosphor exhibited good thermal stability and the corresponding activation energy ΔE was reckoned to be 0.24eV. Upon excitation at 365nm, the internal quantum efficiency of the optimized KMg4(PO4)3:Eu2+ was estimated to be 50.44%. The white N-UV LEDs was fabricated via KMg4(PO4)3:Eu2+, green-emitting (Ba,Sr)2SiO4:Eu2+, and red-emitting CaAlSiN3:Eu2+ phosphors with a near-UV chip. The excellent color rendering index (Ra = 96) at a correlated color temperature (5227.08K) with CIE coordinates of x = 0.34, y = 0.35 of the WLED device indicates that KMg4(PO4)3:Eu2+ is a promising blue-emitting phosphor for white N-UV light emitting diodes (LEDs).

Structure, luminescence property and energy transfer behavior of color-adjustable La5Si2BO13:Ce3+,Mn2+ phosphors

A series of color-adjustable phosphors La5Si2BO13(LSBO):Ce3+,Mn2+ were synthesized through a high temperature solid-state method. The crystal structures of Ce3+ and Mn2+ doped La5Si2BO13 phosphors were refined by the Rietveld method, which were proved to be the apatite-type hexagonal phase (space group of P63/m). It was found that two different La3+ sites in the La5Si2BO13 phase were occupied evenly by Ce3+ and Mn2+ ions, and then the formed vacancy contributed to the charge compensation. La5Si2BO13:Ce3+,Mn2+ phosphors exhibited a broad excitation band ranging from 250 to 375 nm and two broad emission bands centred at 418 nm and 585 nm upon 345 nm excitation. It is found that the emission colors could be tuned from blue-violet (0.1629, 0.0523) to pink (0.3227, 0.1830) by changing the ratio of Ce3+/Mn2+. Moreover, the energy transfer mechanism was verified to be the dipole–dipole interaction, and the critical distance was calculated to be 10.02 A by using the concentration quenching method.

A novel single-phase white light emitting phosphor Ca9La(PO4)5(SiO4)F2:Dy3+: synthesis, crystal structure and luminescence properties

A novel single-phase white light emitting phosphor Ca9La(PO4)5(SiO4)F2:Dy3+ was prepared through traditional high-temperature solid state technology. The crystal structures of Ca9La(PO4)5(SiO4)F2 with or without Dy3+ ions were refined by the Rietveld method. The diffuse reflection spectra, excitation spectra, emission spectra, and decay times were characterized to investigate the photoluminescence properties for application in white light-emitting diodes. The results showed that the Ca9La(PO4)5(SiO4)F2:Dy3+ phosphor could efficiently assimilate n-UV light and emit blue (∼485 nm) and yellow light (∼580 nm), originating from the f–f transitions of Dy3+. The critical Dy3+ quenching concentration (QC) was determined to be about 15 mol%, and the corresponding QC mechanism was verified to be the dipole–dipole interaction. Additionally, the emission colors of all samples were located close to the ideal white light region, and the optimal chromaticity coordinates and correlated color temperature (CCT) were determined to be (x = 0.338, y = 0.336) and 5262 K. All the above results indicate that the as-prepared Ca9La(PO4)5(SiO4)F2:Dy3+ phosphor could serve as a promising candidate for white-light n-UV-LEDs.

The luminescence properties of novel α-Mg2Al4Si5O18:Eu2+ phosphor prepared in air

The α-Mg2Al4Si5O18:Eu2+ phosphor was firstly prepared via the conventional high temperature solid-state reaction method and the reduction of Eu3+ to Eu2+ in air was observed in α-Mg2Al4Si5O18:Eu. The phase structure, photoluminescence (PL) properties, the PL thermal stability and the fluorescence decay curves of the samples were investigated, respectively. Emission and excitation spectra were employed to detect the presence of Eu2+ ions in the compound. Under the excitation at 365 nm, the phosphor exhibited a broad-band blue emission with peak at 463 nm, which was ascribed to the 4f–5d transition of Eu2+. It was further proved that the dipole–dipole interactions resulted in the concentration quenching of Eu2+ in α-Mg2Al4Si5O18:xEu2+ phosphors. When the temperature was increased to 150 °C, the emission intensity of the α-Mg2Al4Si5O18:0.12Eu2+ phosphor was 59.07% of the initial value at room temperature. The activation energy ΔE was calculated to be 0.21 eV, which proved the good thermal stability of the sample. All the properties indicated that the blue-emitting α-Mg2Al4Si5O18:Eu2+ phosphor has potential application in white LEDs.

Design of a Yellow-Emitting Phosphor with Enhanced Red Emission via Valence State-control for Warm White LEDs Application.

The phosphor-converted warm W-LED have being rapidly developed due to the stringent requirements of general illumination. Here, we utilized a strategy to synergistically enhance the red region and emission intensity of novel Eu-activated yellow-emitting LaSiO2N phosphors. This was realized by predicting optimum crystal structure, and governing the concentration of doping ions as well as preparation temperature. By using these straight-forward methods, we were able to vary the valence to enhance the red region and improve the quantum efficiency of LaSiO2N phosphor. The warm W-LED lamp fabricated with this red region enhanced LaSiO2N:Eu phosphor exhibited high CRI (Ra = 86), suitable CCT (5783 K) and CIE chromaticity (0.33, 0.36), indicating this synergistically enhanced strategy could be used for design of yellow-emitting phosphor materials to obtain warm W-LEDs.

Structure and photoluminescence properties of red-emitting apatite-type phosphor NaY 9 (SiO 4 ) 6 O 2 :Sm 3+ with excellent quantum efficiency and thermal stability for solid-state lighting

A novel red-emitting phosphor NaY9(SiO4)6O2:Sm3+ (NYS:Sm3+) was synthesized and the X-ray diffraction and high-resolution TEM testified that the NYS compound belongs to the apatite structure which crystallized in a hexagonal unit cell with space group P63/m. The novel phosphor boasts of such three advantageous properties as perfect compatible match with the commercial UV chips, 73.2% quantum efficiency and 90.9% thermal stability at 150 °C. Details are as follows. NYS:Sm3+ phosphor showed obvious absorption in the UV regions centered at 407 nm, which can be perfectly compatible with the commercial UV chips. The property investigations showed that NYS:Sm3+ phosphor emitted reddish emission with CIE coordination of (0.563, 0.417). The optimum quenching concentration of Sm3+ in NYS phosphor was about 10%mol, and the corresponding concentration quenching mechanism was verified to be the electric dipole–dipole interaction. Upon excitation at 407 nm, the composition-optimized NYS:0.10Sm3+ exhibited a high quantum efficiency of 73.2%, and its luminescence intensity at 150 °C decreased simply to 90.9% of the initial value at room temperature. All of the results indicated that NYS:Sm3+ is a promising candidate as a reddish-emitting UV convertible phosphor for application in white light emitting diodes (w-LEDs).

Tunable Upconversion Luminescence and Energy Transfer Process in BaLa2ZnO5:Er3

BaLa2ZnO5:Er3+/Yb3+ has been synthesized via a high temperature solid-state method, and the tunable upconversion luminescence and energy transfer process between Yb3+ and Er3+ in this system have been demonstrated. Upon 980 nm laser excitation, the intense green and red emission around 527, 553, and 664 nm were observed for BaLa2ZnO5:Er3+/Yb3+, which can be assigned to the characteristic energy level transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 of Er3+, respectively. The critical Er3+ quenching concentration (QC) was determined to be about 5 mol%, and the power studies indicated that mixture of 2- and 3-photon process was responsible for the green and red upconversion luminescence.

Luminescence properties and energy transfer investigations of Ba2La2.85−xTb0.15Eux(SiO4)3F multicolor phosphor

The Ba2La2.85−xTb0.15Eux(SiO4)3F (BLSOF:0.15Tb3+, xEu3+) multicolor phosphors with apatite structure were synthesized via the solid-state pathway. The crystal structure and luminescence properties of the phosphors were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Rietveld refinement, photoluminescence excitation (PLE) and photoluminescence (PL). The luminescence performance of the phosphor was optimum when the concentration of Tb3+ was set to be 0.15 mol and the concentration of Eu3+ was set to be 0.22 mol. Under the accurate excitation of 373 nm near ultraviolet (n-UV) light, the emitting color of the phosphors can be tuned from green to red with increasing Eu3+/Tb3+ ratio. It was further proved that the quadrupole–quadrupole (q–q) interaction is responsible for the energy transfer (ET) in the BLSOF:0.15Tb3+, 0.22Eu3+ phosphor. Owing to the excellent thermal quenching luminescence property, the BLSOF:0.15Tb3+, xEu3+ phosphor can be applied in n-UV white light emitting diodes (w-LEDs) and serve as the warm part of warm white light.

Crystal structure, thermally stability and photoluminescence properties of novel Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors

A series of novel luminescent phosphors Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} with apatite structure were synthesized via a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples, and the selected Sr{sub 9.97}(PO{sub 4}){sub 6}O:0.03Eu{sup 2+} phosphor exhibits strong thermal quenching resistance, retaining the luminance of 88.73% at 150 °C. The quenching concentration of Eu{sup 2+} in Sr{sub 10}(PO{sub 4}){sub 6}O was about 0.03 attributing to the dipole–quadrupole interaction. The Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphor exhibited a broad-band blue emission at 439 nm upon excitation at 346 nm. The results indicate that Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Graphical abstract: Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Highlights: • Sr{sub 9.97}(PO{sub 4}){sub 6}O:0.03Eu{sup 2+} phosphor exhibits strong thermal quenching resistance. • Two different Eu{sup 2+} emission centers exists in Sr{sub 10}(PO{sub 4}){sub 6}O. • The activation energy was also estimated for the Eu{sup 2+} luminescence center.