UV-pumped Light-emitting Diodes Research Articles

Phase control in the synthesis of cesium copper iodide compounds for their photoluminescence and radioluminescence study

Lead-free metal halide perovskites have attracted much attention owing to their non-toxicity and excellent optical properties. Especially, cesium copper iodide compounds exhibit advantages of good environmental stability and low cost, rendering promising potential applications in optoelectronic devices field. Here, we use an anti-solvent assisted crystallization method to realize phase control syntheses of CsCu2I3 and Cs3Cu2I5 by varying the concentrations of precursor solution. Using high precursor solution concentrations, Cs3Cu2I5 with strong blue emission peak at 440 nm is prepared. While the CsCu2I3 is fabricated at low precursor solution concentrations, with the yellow emission peak of 580 nm. Furthermore, the UV-pumped light-emitting diodes (UV-LEDs) are realized by adopting CsCu2I3 and Cs3Cu2I5 powders as phosphors, and we also obverse the scintillation characteristic of the cesium copper iodide powders, showing potential applications for lighting and X-ray detection devices.

Mesoporous Aluminum Hydroxide Synthesized by a Single-Source Precursor-Decomposition Approach as a High-Quantum-Yield Blue Phosphor for UV-Pumped White-Light-Emitting Diodes.

Strongly emissive (photoluminescence quantum yield up to 65%), thermally stable aluminum hydroxide blue phosphors are synthesized by a single-source precursor-decomposition approach. Blue-emitting UV-pumped light-emitting diodes (LEDs) based on the aluminum hydroxide phosphor reach luminous efficiency of 27.5 lm W-1 , while UV-white-LEDs integrating blue-emitting aluminum hydroxide and red-emitting CuInS2 nanocrystals achieve high color-rendering-index values of 94.3 and luminous efficiency of 23.5 lm W-1 .

A novel green-emitting phosphor Ba2Gd2Si4O13:Eu(2+) for near UV-pumped light-emitting diodes.

A novel green-emitting phosphor Ba2Gd2Si4O13:Eu(2+) has been prepared using a conventional high-temperature solid-state method. X-ray diffraction and photoluminescence spectra were used to characterize the as-synthesized phosphor. The Ba2Gd2Si4O13:Eu(2+) phosphor exhibits a broad emission band centered at 503 nm under 365 nm excitation. Monitoring the 503 nm emission, the Ba2Gd2Si4O13:Eu(2+) phosphor shows an intense broad excitation band ranging from 200 to 410 nm. The concentration quenching mechanism has been investigated, and demonstrated to involve a dipole-dipole interaction. The critical concentration was found to be about 4 mol%. The critical distance calculated using the concentration method and spectral overlap method was 23.9 Å and 27.1 Å, respectively. The temperature-dependent photoluminescence and CIE chromaticity coordinate of the Ba2Gd2Si4O13:Eu(2+) phosphor were also investigated in this work. The results revealed that Ba2Gd2Si4O13:Eu(2+) possesses excellent thermal stability and the CIE value of the Ba2Gd2Si4O13:0.04 Eu(2+) phosphor upon 365 nm excitation is (0.211, 0.434), located in the green region. All the properties indicate that the Ba2Gd2Si4O13:Eu(2+) phosphor is a potential green-emitting phosphor fit for ultraviolet light pumped LEDs.

Photoluminescence properties of red phosphor Gd3PO7:Eu3+ for UV-pumped light-emitting diodes

A red-emitting Gd3PO7:5% Eu3+ phosphor is reported. Through transitions of 5d -> 4f (F-7(1) and F-7(2)) in Eu3+, the phosphor shows a bright red emission under ultraviolet (UV) light excitation. The emission intensity at 615 nm corresponding to D-5(0) -> F-7(2) transition of Eu3+ ion depending on irradiation time under 394 nm excitation increases firstly and then small reduces. After 20 min for UV-light irradiation, it decreases by about 0.5% suggesting that the photostability of the red phosphor Gd3PO7:Eu3+ is excellent. Under 325 nm excitation, the emission intensities grow rapidly as the temperature increases from 75 K to 285 K and then it keeps on growing slowly until 475 K, revealing the excellent thermostability of the red phosphor Gd3PO7:Eu3+. Decay time and time-resolved luminescence measurements have also been studied. All the results reveal that Gd3PO7:Eu3+ is a promising red-emitting phosphor for UV LED applications. (c) 2013 Elsevier B.V. All rights reserved.

Blue–white–orange color-tunable luminescence of Ce3+/Mn2+-codoped NaCaBO3via energy transfer: potential single-phase white-light-emitting phosphors

Ce3+/Mn2+-codoped NaCaBO3 single-phase color-tunable phosphors were synthesized by solid-state reaction, and their photoluminescence properties were investigated in detail. Under UV excitation, two main emission bands peaking at 400 and 610 nm were realized in the NaCa0.89BO3: 0.01Ce3+, 0.10Mn2+ phosphor on the basis of the energy transfer from Ce3+ to Mn2+ with an efficiency of over 83%. The energy transfer was validated and demonstrated to be a resonant type via a dipole–dipole mechanism, and the critical distance RC values calculated by the quenching concentration method and the spectral overlap method were 22.85 and 19.41 A, respectively. On examining the Mn2+-concentration-dependent photoluminescence properties, it was observed that the emission color could be tuned from blue (0.162, 0.031) to white-light (0.335, 0.259) and eventually to orange (0.489, 0.246) through energy transfer by changing the Ce3+/Mn2+ ratio. Combining a 370 nm UV chip and a single-phase white-emitting NaCa0.96BO3: 0.01Ce3+, 0.03Mn2+ phosphor produced a white light-emitting diode with CIE chromaticity coordinates of (0.326, 0.274) and an excellent color rendering index of 90.7 at a correlated color temperature of 4046 K. These results indicate that the NaCaBO3: Ce3+, Mn2+ phosphors have potential applications as single-phase white-light-emitting phosphor-converted materials for UV-pumped light-emitting diodes.

Eu2+-doped pollucite CsAlSi2O6 with High luminescence efficiency for UV-pumped light-emitting diodes

A new phosphor of Eu2+-doped pollucite CsAlSi2O6 was synthesized by conventional solid-state reaction. The photoluminescence (PL) excitation and emission spectra were measured. The phosphors can be efficiently excited by near-UV light and show broad luminescence spectra with the main emission peak at around 450nm corresponding to 5d–4f transition of Eu2+ ions. CsAlSi2O6:0.05Eu2+ exhibits the brightest blue–green emission with CIE coordinates (x=0.21, y=0.32) and a quantum efficiency of 67%. The dependence of the luminescence intensity of CsAlSi2O6:Eu2+ on temperatures was investigated. The activation energy (ΔE) for thermal quenching was reported.

High efficiency blue-emitting phosphor: Ce3+-doped Ca5.45Li3.55(SiO4)3O0.45F1.55 for near UV-pumped light-emitting diodes

A novel blue-emitting phosphor, Ca5.45Li3.55(SiO4)3O0.45F1.55:Ce3+, was synthesized by a solid-state reaction, and the phase formation, crystal structure and luminescence properties were investigated in detail. The Ca5.45Li3.55(SiO4)3O0.45F1.55:Ce3+ phosphor shows a highly intense blue emission peaking at about 470 nm upon near-ultraviolet (n-UV) excitation, which corresponds to the Ce3+ luminescence center substituting the seven-coordinated Ca2+ sites in the lattice. The critical quenching concentration of Ce3+ in the Ca5.45Li3.55(SiO4)3O0.45F1.55:Ce3+ phosphor was about 3 mol%, and the corresponding concentration quenching mechanism was verified to be the dipole–dipole interaction. Upon excitation at 365 nm, the composition-optimized Ca5.42Li3.55(SiO4)3O0.45F1.55:0.03Ce3+ exhibited a high quantum efficiency of 82%, and its luminescence intensity at 150 °C decreases to 71% of the initial value at room temperature. The above results indicate that Ca5.45Li3.55(SiO4)3O0.45F1.55:Ce3+ is a promising candidate as a blue-emitting n-UV convertible phosphor for application in white light emitting diodes (w-LEDs).