A series of Dy3+-, Tm3+-, Eu3+-coactivated KSr4(BO3)3 phosphors were synthesized via a standard solid-state reaction under normal ambient air, and the emission colors could be tuned from blue to yellow and then to red, including almost all the white light region, through tuning the energy transfer. It was discovered that the energy is transferred from Tm3+ to Dy3+ by: directly observing overlap of the excitation spectrum of Dy3+ and the emission spectrum of Tm3+; the systematic relative decline and growth of emission bands of Tm3+ and Dy3+, respectively; and faster decay times of the blue emissions from energy donors. The resonance-type energy transfer from Tm3+ to Dy3+ was demonstrated to be via the dipole–quadrupole mechanism and the critical distance of energy transfer was calculated to be 20.7 A. Rietveld refinements of the crystal structures of the products obtained from powder X-ray diffraction (XRD) elucidated a preferable occupancy in the crystal unit for the doped rare-earth cations, which well explained the formation of the Tm3+–Dy3+ close pair. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content, KSr4(BO3)3:Dy3+,Tm3+,Eu3+ phosphors exhibit great potential for use as single-component phosphors for warm white ultraviolet light-emitting diodes (UV LEDs).

Luminescence and energy transfer of a color tunable phosphor: Dy3+-, Tm3+-, and Eu3+-coactivated KSr4(BO3)3 for warm white UV LEDs

Synthesis, photoluminescence, cathodoluminescence, and thermal properties of novel Tb3+-doped BiOCl green-emitting phosphors

Excellent photoluminescence and cathodoluminescence properties in Eu3+-activated Sr2LaNbO6 materials for multifunctional applications

To alleviate the issues of low thermal stability and high correlated color temperature, exploring an inorganic color converter with both yellow- and red-emissions to replace the conventional resin/silicone-based phosphor converter for obtaining high-power warm white light-emitting diodes is highly desired. In this study, a series of garnet-based Li6CaLa2−2xEu2xSb2O12 (x = 0.1–1.0) red phosphors have been successfully synthesized by a conventional high-temperature solid-state method. The microstructure and luminescence properties were systematically investigated by X-ray diffraction, emission/excitation spectra, luminescence lifetimes and temperature-dependent decays. The as-synthesized phosphors exhibited a highly efficient red luminescence at 611 nm corresponding to the 5D0–7F2 electric dipole transition of Eu3+, and the luminescence monotonously enhanced as the Eu3+ content was increased to 100 mol%. The absence of concentration quenching was ascribed to the large Eu3+–Eu3+ distance (7.048–7.105 A) and subsequently the hindering of unwanted energy migration among them in the Li6CaLa2Sb2O12 crystalline lattice. Impressively, the Li6CaLaEuSb2O12 phosphor showed an excellent thermal stability with only 9.7% emission loss when the recording temperature was increased from 293 K to 553 K. To evaluate the suitability of Li6CaLa2Sb2O12:Eu3+ as a red converter, both the garnet-based Y3Al5O12:Ce3+ yellow and Li6CaLa2Sb2O12:Eu3+ red phosphor co-doped glass ceramics were successfully fabricated by a low-temperature co-sintering technique. Importantly, the adverse energy transfers between Ce3+ and Eu3+ were efficiently suppressed due to the spatial separation of Ce3+ in Y3Al5O12 and Eu3+ in Li6CaLa2Sb2O12 in the crystal lattice. As a consequence, the quantum yield of the glass ceramic reached as high as 89.3%, and the constructed white light-emitting diode exhibited an optimal luminous efficacy of 101 lm W−1, a correlated color temperature of 5449 K and a color rendering index of 73.7. It is expected that the developed Li6CaLa2−2xEu2xSb2O12 red phosphors and the related glass ceramics should have potential applications in high-power warm white light-emitting diodes.

Garnet-based Li6CaLa2Sb2O12:Eu3+ red phosphors: a potential color-converting material for warm white light-emitting diodes

Synthesis and luminescent properties of Eu3+-activated Na0.5Gd0.5MoO4: A strong red-emitting phosphor for LED and FED applications

A series of Ba2ZnB2O6:Eu3+ phosphors with a red-emitting band centered at 616 nm were prepared by traditional high temperature solid-state reaction methods. The site-preferred occupancy of Eu3+ in Ba2ZnB2O6 and luminescence properties of Ba2ZnB2O6:Eu3+ were studied combined with X-ray diffraction (XRD), photoluminescence excitation (PLE) spectra and emission (PL) spectra as well as temperature-dependent PL and decay curves. The Rietveld refinements indicate that the Eu3+ ions prefer to occupy Zn (1) (4a) and Zn (2) (4a) sites simultaneously. The PL intensity is improved with increasing Eu3+ content and the optimal dopant content is 0.05. The temperature-dependent PL spectra indicate that the emission intensity decreases with the temperature because of the enhancement of the non-radiative transition. The PL emission intensities of Ba2ZnB2O6:0.05Eu3+ phosphors with Li+, Na+ and K+ as charge compensators are enhanced significantly, and the phosphor compensated by Li+ ions emits the strongest emission. The Commission Internationale de I'Eclairage (CIE) color coordinates of Ba2ZnB2O6:0.05Eu3+ are very close to the CIE of standard red light.

Site occupancy and photoluminescence properties of Eu3+-activated Ba2ZnB2O6 phosphor

Mn2+-activated red phosphor α-LiZnBO3:Mn2+ was synthesized by solid state reaction. ESR spectra prove that the doped ions are Mn2+. The doped Mn2+ ion is inclined to occupy Zn2+ site, which is a tetrahedral coordination. The diffuse reflection spectra indicate that α-LiZnBO3:Mn2+ has strong absorption in the range of 400–450 nm. Excited at 431 nm, an abnormal red emission band in the wavelength of 550–800 nm is observed, which is because of the strong crystal field induced by the distorted tetrahedral. The emission bands are centered at 647 nm, regardless of the excitation wavelength and Mn2+ doping concentration. The temperature-dependent PL results reveal that α-LiZnBO3:Mn2+ is thermally stable but the emission peak moves to shorter wavelength as temperature increases because of the decrease of the crystal field.

Abnormal luminescent property of Mn2+ in α-LiZnBO3:Mn2+

The influences of process parameters and Fe diffusing into Cu(In,Ga)Se2 (CIGS) films on the orientation of CIGS absorbers grown on the stainless steel (SS) foils are investigated. The structural properties, morphology, and elemental profiles are characterized using X-ray diffraction, scanning electron microscopy, and second ion mass spectroscopy, respectively. The orientation of CIGS thin films on the SS substrates strongly depends on the texture of the (In,Ga)2Se3 precursor, determined by the substrate temperature at the first stage (Ts1) and the flux ratio of Se to (In + Ga). Among these factors, Ts1 is the prerequisite to achieve [300]-oriented IGS layer, which will yield [200]-oriented CIGS thin film in the later process. The results indicate that through the comparison of CIGS thin films on the Mo/SS substrates and on the Mo/ZnO/SS substrates and combined with simply calculation, Fe diffusing into the CIGS layer will hinder the growth of the CIGS grains along [112] orientation. The grazing-incidence X-ray diffraction results suggest that the surface of the [220]-textured CIGS thin film on the SS substrate still has [220] predominance, whereas the surface texture of the [220]-texture CIGS thin film on the Mo/soda-lime glass substrate became [112] predominant, which is due to the different compensation ability between Fe and Na elements. Finally, the relations between the device parameters and the degrees of the preferred orientation of CIGS absorbers are investigated. Copyright © 2012 John Wiley & Sons, Ltd.

Preferred orientation of Cu(In,Ga)Se2 thin film deposited on stainless steel substrate

The role of growth temperature and Se flux on Cu(In,Ga)Se2 (CIGS)/Mo deposited on stainless steel substrates without a barrier is investigated by combined use of secondary ion mass spectroscopy, scanning electron microscopy and Raman spectroscopy. Fe atoms diffuse into the CIGS film with an increasing slope toward the CIGS front surface and the CIGS/Mo interface at 500 °C. High Se flux can increase the grain size and depress the formation of group III-rich phases on the surface and grain boundaries of the CIGS film, reducing Fe content in the surface region of the CIGS film and grain boundaries, which results in the increase of open circuit voltage (Voc) and fill factor (FF). Meanwhile, Jsc also significantly increases for high Se flux. In this case, a 12.1%-efficient CIGS solar cell on stainless steel without a diffusion barrier and Na supply is obtained. The influence of diffusing Fe on a solar cell with different Se fluxes is further discussed in detail.

http://iopscience.iop.org/article/10.1088/0268-1242/27/6/065007/pdf

The role of growth temperature and Se flux on Cu(In,Ga)Se2 thin film deposited on a stainless steel substrate and solar cell

We have synthesized a Eu3+-activated KSr4(BO3)3 red phosphor by solid state reactions. Rietveld refinement on X-ray diffraction data indicates that Eu3+ ions are inclined to occupy Sr(2) (8c) site in the structure of KSr4(BO3)3. The composition-optimized KSr4(BO3)3:Eu3+ exhibits a dominant emission peak at 612 nm (5D0-7F2) with CIE coordinates of (0.64, 0.35) under the excitation at 394 nm. By codoping M+ ions (M = Li, Na, and K) in KSr4(BO3)3:Eu3+ to compensate the charge unbalance, the intensities of emission spectra at 612 nm can be increased greatly, but the CIE coordinates will not be changed. The red-emitting KSr4(BO3)3:Eu3+ phosphor may be potential candidate in the fabrication of white light-emitting diodes (LEDs).

Structure and photoluminescence properties of KSr_4(BO_3)_3:Eu^3+ red-emitting phosphor

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