Study on luminescence properties of Ce3+ and Eu3+ ions in nanocrystalline hexagonal Zn4 Al22 O37 novel system

The present communication is strongly focused on an investigation of synthesis, structural and luminescence properties of cerium (Ce³⁺ ) and europium (Eu³⁺ ) activated Zn₄ Al₂₂ O₃₇ phosphors. We have prepared Ce³⁺ and Eu³⁺ doped Zn₄ Al₂₂ O₃₇ novel phosphors by using solution combustion synthesis route. The structural properties have been studied by using powder x-ray diffraction (XRD) and high resolution transverse electron microscope (HR-TEM). The optical properties are studied by using ultraviolet visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT-IR) and luminescence properties are studied using photoluminescence technique (PL). The crystal structure of the prepared Zn₄ Al₂₂ O₃₇ host and Ce³⁺ and Eu³⁺ activated Zn₄ Al₂₂ O₃₇ phosphors have been investigated and these have found a hexagonal structure. The measured PL emission spectrum of Ce³⁺ doped Zn₄ Al₂₂ O₃₇ phosphor shows an intense and broad emission band centered at 421 nm under the 298 nm excitation wavelength. Whereas, the Eu³⁺ doped Zn₄ Al₂₂ O₃₇ phosphor exhibits two strong and intense emission bands around 594 nm (orange) and 614 nm (red), monitored under 395 nm excitation. The CIE color coordinates of the Ce³⁺ doped Zn₄ Al₂₂ O₃₇ have been investigated as x=0.1567, y=0.0637 (blue) at 421 nm and Eu³⁺ doped Zn₄ Al₂₂ O₃₇ as x= 0.6018, y= 0.3976 (orange) at 594 nm and x= 0.6779, y= 0.3219 (red) at 614 nm emissions. The luminescence behavior of the synthesized phosphors suggested that these phosphors may be applicable in lighting applications.

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability

Eu³⁺-activated Ba₂Y₅B₅O₁₇ (Ba₂Y_5−xEu_xB₅O₁₇; x = 0.1–1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba₂Y_5−xEu_xB₅O₁₇ showed red emission peaking at 616 nm which was attributed to the ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺ ions. Meanwhile, the influences of different concentrations of Eu³⁺ ions on the PL intensity were also discussed. The optimum concentration of Eu³⁺ ions in the Ba₂Y_5−xEu_xB₅O₁₇ phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole–dipole interaction and the critical distance (R_c) for energy transfer among Eu³⁺ ions was determined to be 5.64 Å. The asymmetry ratio [(⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁)] of Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba₂Y_5−xEu_xB₅O₁₇ phosphors. In addition, the CIE color coordinates of the Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba₂Y_4.2Eu_0.8B₅O₁₇ sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

A novel Ba₂Y₅B₅O₁₇:Eu³⁺ red-emitting phosphor with high color purity, high quantum efficiency and excellent thermal stability was developed.

Eu3+-doped Bi4Si3O12 red phosphor for solid state lighting: microwave synthesis, characterization, photoluminescence properties and thermal quenching mechanisms

Europium-doped bismuth silicate (Bi₄Si₃O₁₂) phosphor has been prepared by microwave irradiation method and its crystal structure is determined using Rietveld method. As-prepared phosphor consists of spherical, monodispersed particles with few agglomeration, high crystallinity, and narrow grain size distribution. The phosphor can be efficiently excited in the wavelength range of 260-400 nm, which matched well with the emission wavelengths of NUV LED chips. The photoluminescence spectra exhibit the highest emission peak at 703 nm originating from ⁵D₀ → ⁷F₄ transition of Eu³⁺ under NUV excitation. The luminescence lifetime for Bi₄Si₃O₁₂: 2 at% Eu³⁺ phosphor decreases from 2.11 to 1.86 ms with increasing temperature from 10 to 498 K. This behavior of decays is discussed in terms of radiative and nonradiative decays dependence on temperature. The thermal quenching mechanism of ⁵D₀ emission of Eu³⁺ in Bi₄Si₃O₁₂ phosphor is a crossover process from the ⁵D₀ level of Eu³⁺ to a ligand-to-europium (O^2- → Eu³⁺) charge transfer state. The quantum efficiency of the phosphor under 393 nm excitation is found to be 14.5%, which is higher than that of the commercial red phosphors Y₂O₃: Eu³⁺, Y₂O₂S: Eu³⁺. The temperature effect on CIE coordinate was discussed in order to further investigate the potential applications.

Electrospraying magnetic-fluorescent bifunctional Janus PLGA microspheres with dual rare earth ions fluorescent-labeling drugs

Magnetic-fluorescent Janus PLGA microspheres [PLGA/EuLa₃(Bim)₁₂]//[PLGA/Fe₃O₄] with dual rare earth ions fluorescent-labeling drug could provide accuracy and efficiency for fluorescent tracing.

Long persistent phosphors—from fundamentals to applications

We present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, material kinds, and applications of long persistent phosphors.