The different Mg/Zn ratios of (Mg1−xZnx)2.97(PO4)2:0.03Mn2+ result in various PL intensities and spectra profiles, which are related to the crystal field strength and local environment of the Mn2+ ions.
LiSiON:Eu2+, Eu2+/Mn2+ phosphors with compositions of Li1-2x-2yEuxMnySiON (x = 0−0.006, y = 0−0.006) were successfully fabricated using Li4-2x-2ySiO4:xEu2+, yMn2+ and Si3N4 as starting materials. The crystal and electronic structures, as well as the luminescence properties of Li1-2x-2ySiON:xEu2+, yMn2+ were reported. First-principles calculations indicated that LiSiON host was an insulator with indirect band gap about 5.4 eV, which was in good agreement with the experimental data obtained from the diffuse reflection spectrum. The value of x in Li1-2xEuxSiON gave rise to obvious differences in the emission profiles and peak wavelength which might result from the different crystal environments around Eu2+ ions. The mechanism of energy transfer from a sensitizer Eu2+ ion to an activator Mn2+ ion in LiSiON:Eu2+,Mn2+ phosphors were demonstrated to be electric dipole-quadrupole interaction. The emission hue of Li1-2x-2ySiON:xEu2+, yMn2+ varied from blue (0.232, 0.296) (x = 0.001, y = 0) to white-light (0.329, 0.316) (x = 0.001, y = 0.004) by tuning the Eu2+/Mn2+ ratio. Preliminary studies showed that the LiSiON:Eu2+, Eu2+/Mn2+ might be a promising white-light-emitting phosphor for ultraviolet (UV) based white Light Emitting Diodes (LEDs).
Single-phased Y 2−x Si 3 O 3 N 4 :xCe 3+ (0 < x ≤ 0.4) phosphors were prepared by solid-state reaction method in flowing hydrogen and nitrogen mixture gas. The X-ray diffraction analysis indicated that Ce 3+ ions had been incorporated into the host lattice of Y 2 Si 3 O 3 N 4 , and the optimized doping concentration was 3 mol%. Strong absorption peaking at about 397 nm was observed on the excitation spectra for the Ce 3+ -doped phosphors, which matched well with the current near-ultraviolet (NUV) InGaN/GaN light emitting diodes (LEDs). The Y 2−x Ce x Si 3 O 3 N 4 samples showed a broad emission band with peak wavelength ranging from 465 to 500 nm, which was attributed to the 5d-4f transition of Ce 3+ . Energy transfer between Ce 3+ ions was discussed and evidenced in detail, which resulted in redshift of the emission and concentration quenching. To understand the thermal quenching behavior, the temperature-dependent luminescence of Y 1.94 Ce 0.06 Si 3 O 3 N 4 was investigated. Bluish-green LEDs was fabricated by integrating a near-ultraviolet (NUV) chip with Y 1.94 Si 3 O 3 N 4 :0.06Ce 3+ phosphor as a single package.
A series of Ca3La3(1-x)Eu3x(BO3)5 phosphors were prepared via a solid-state reaction under reducing atmosphere. Rietveld refinements were performed by adopting the powder X-ray diffraction data, which indicates the occupations of Eu3+ on both La3+ and Ca2+ sites with a preferred location on the La3+ site over the Ca2+ site. This kind of phosphors could be excited by UV and blue LED in solid-state lighting technology and the CIE chromaticity coordinates for phosphors CLBO: 0.06Eu3+ (λex = 254 nm) and CLBO: 0.12Eu3+ (λex = 393 nm) are (0.6712, 0.3328) and (0.6685, 0.3287), respectively, which are compliant with the national television system committee (NTSC) standard for red chromaticity. The energy transfer rate between the Eu3+-Eu3+ pairs is weak that proved by the results of the decay process and the efficiency of the Eu3+ 5D0→7F2 emission. The mechanism responsible for the non-reduction of Eu3+ was analyzed, which was determined by two factors: 1) no element of the host matrix can be oxidized and 2), cationic vacancies which can be regarded as the electron donor cannot exist. The temperature dependence study shows thermal quenching behavior is attributed to crossover from the 5D0 excited state of the Eu3+ to the charge transfer state band and these phosphors have good thermal stability.
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