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In this work, using β-Ca3(PO4)2 as a structural model, a series of [Ca9Na3xY1−x(PO4)7 (CNYPO-I, 0 ≤ x ≤ 1/2) ← Ca3(PO4)2 → Ca9+yNa3/2−y/2Y(1−y)/2(PO4)7 (CNYPO-II, 0 ≤ y ≤ 1)] phosphors were prepared using a cationic heterovalent substitution approach. The substitution of Y3+ and Na+ for Ca2+ led to a redistribution of Eu2+ within the lattice and was accompanied by changes to the corresponding luminescence behavior. As the x and y values increased, the vacancies in the structure were gradually occupied by Na+ to form Na(4) sites that are conducive to Eu2+ occupation. When y = 1, the vacancies were completely occupied, and the Eu2+ emission peaks from Ca(1/2) and Ca(3) sites showed a significant blue shift. The underlying mechanism of that shift is discussed. The CNYPO-I (x = 0) sample displayed the best thermal stability; the effects of vacancies, thermal ionization and cross-over mechanism on thermal quenching are also discussed. As x and y increase, the thermal stability of the samples gradually decreased. Eu2+ and Mn2+ co-doped CNYPO-I (0 ≤ x ≤ 1/2) and CNYPO-II (0 ≤ y ≤ 1) phosphors achieved full coverage of the visible light region (400–800 nm). These white LEDs have relatively high color-rendering indexes (>80) and adjustable color temperatures from 2854–7000 K. This work provides an effective strategy for designing novel luminescent materials and realizing multi-site adjustment of activator ions. [ABSTRACT FROM AUTHOR]

Designing two-step tuning based on substitution of multiple cation lattices and energy transfer successfully achieved versatile colour output for single-phase phosphor-converted white LEDs in this work. Herein, we chose whitlockite-type Ca9LiY0.667(PO4)7 compound as a host which provides multiple cation sites for Eu2+ occupation. Spectral results indicate that the Ca9LiY0.667(PO4)7:Eu2+ phosphor emits a cold white emission due to its multiple emission bands at about 420, 480, and 530 nm, which correspond to emissions from the M(3), M(1)/M(2) and M(5) cation sites as ascertained by the Rietveld refinement method. In order to enhance the red emission of CLYPO:Eu2+ phosphors, they were codoped with Mn2+. Warm white emission in a single-phase host based on energy transfer was successfully obtained in the CLYPO:Eu2+,Mn2+ phosphors. The excitation band of the CLYPO:Eu2+,Mn2+ phosphors in the 360 to 450 nm range perfectly coincides with that of commercial LED chips, implying that these phosphors are desirable for white LED applications. White LEDs with a higher color rendering index (Ra = 90.2) and a lower correlated color temperature (CCT = 3614 K) were achieved by using a single-phase CLYPO:0.03Eu2+,0.10Mn2+ phosphor and a 395 nm InGaN-LED chip. [ABSTRACT FROM AUTHOR]

The red-emitting Ca9Eu(PO4)7 nanophosphors have been successfully synthesized by a facile hydrothermal method. X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, GSAS structural refinement and scanning electron microscopy (SEM) were used to characterize the materials. Rietveld refinement of powder X-ray diffraction patterns of Ca9Eu(PO4)7 demonstrated that the structure of Ca9Eu(PO4)7 consisted of [PO4] tetrahedra. Ca/Eu atoms filled the space between the tetrahedral groups with Eu3+ ions distributed randomly on three individual Ca crystallographic sites. The major red emission peak located at 616 nm under 397 nm excitation attributed to the electric dipole transition 5D0→7F2 of Eu3+ was a parity forbidden f–f configuration transition, which would only occur when Eu3+ occupied lattice sites without inversion symmetry. Introducing Gd, La, and Y ions into samples made luminescence properties of Ca9Eu1−xLnx(PO4)7 (Ln = Gd, La, Y) phosphors decrease. pH value plays a key role in the formation of Ca9Eu(PO4)7 nanophosphor morphology. With increasing pH in the initial reaction solution, the morphology of samples changed from rod to sphere and their aspect ratio also decreased. Different morphologies have different photoluminescence properties, and samples prepared at pH 7 manifested better photoluminescence properties relative to other samples. This novel red-emitting phosphor could be applied in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A novel phosphate Ca9La(GeO4)0.75(PO4)6 was investigated to add to the family of phosphate phosphors and application in LEDs. In this work, the single phase red-emission Ce3+,Mn2+ co-doped phosphate Ca9La(GeO4)0.75(PO4)6 phosphor was synthesized by the solid-state reaction from both theoretical and practical points of view. The crystal structure was determined by Rietveld refinement and TEM. Its cell parameters are a = b = 10.4077605(2) Å, and c = 37.4714968(1) Å. The characteristic photoluminescence properties were studied in detail using photoluminescence excitation spectra, emission spectra, decay times and thermal quenching properties. Purple and red broad band emission from Ce3+ and Mn2+ was detected under excitation at 313 nm. According to this research, the Ca9La(GeO4)0.75(PO4)6:Ce3+,Mn2+ phosphor shows high thermal stability in the red-emission area. With the increase of the temperature, the intensity ratio of Mn2+ and Ce3+ emission rises rapidly and the purity of red-emission is improved. In order to reasonably explain this special phenomenon, an implicit mechanism between thermal quenching and energy transfer is proposed based on the configurational coordinate diagram. In addition, the mechanism could be helpful for understanding the thermal properties of multiple activators Ce3+ and Mn2+ co-doped phosphors as the reference. [ABSTRACT FROM AUTHOR]

The substituted activator ions Eu2+ in the β-Ca3(PO4)2-type structure, Ca9NaMg(PO4)7 compound, have been studied as emission centers, as well as structural probes. The crystal structure and crystallographic sites of Eu2+ in Ca9NaMg(PO4)7 have been identified by Rietveld refinements, electron paramagnetic resonance (EPR) spectroscopy analysis and combined photoluminescence spectral analysis, respectively. Ca9NaMg(PO4)7:Eu2+ phosphor exhibits a broad emission band in the visible light region with three distinguished peaks centered at 415, 458, and 615 nm, which are ascribed to different Eu2+ emission centers occupied in three different Ca crystallographic sites. The concentration quenching behavior, variation in lifetimes and the temperature dependent luminescence properties have been investigated as a function of different emission centers, 415, 458, and 625 nm for Ca9NaMg(PO4)7:Eu2+ phosphor. Accordingly, the relationship among three different Eu2+ luminescence centers originating from three different Ca2+ crystallographic sites has been found and verified. [ABSTRACT FROM AUTHOR]