Currently, developing single-phased white light phosphors based on a single-doped activator is an efficient approach to blends of bicolor/tricolor phosphors for realizing phosphor-converted white light emitting diodes (pc-WLEDs) with a high color rendering index (CRI) and low correlated color temperature (CCT). Here, we present high CRI (Ra = 93–95) and low CCT (3500–6000 K) white lights by cosubstituting [Ca2+–P5+] for [La3+–Si4+] in the solid solution Ca(8→2)La(2→8)(PO4)6−x(SiO4)xO2:Eu2+/Eu3+ (CLPSO_Eu). The results are attributed to the presence of multi Ca2+ sites due to possible mixing nanophases and the simultaneous occupancy of Ca2+ and La3+ sites by Eu, resulting in the mixing of blue (466 nm) and green emissions (540 nm) for Eu2+, and red emission (613 nm) for Eu3+, which were perfectly confirmed using X-ray Rietveld refinement, photoluminescence spectra and extended X-ray absorption fine structure. These findings not only imply that the as-prepared CLPSO_Eu are promising single-phased white light phosphor for near-UV based WLEDs but also offer a novel avenue to design high CRI white light phosphors based on a tunable Eu2+/Eu3+.

A series of Ca5(PO4)3Cl (CPOCl):Ce3+/Eu2+,Tb3+/Mn2+ phosphors with apatite structures have been prepared via the Pechini sol–gel process. The structure refinement indicates that the as-prepared phosphors crystallized in a hexagonal phase with the space group of P63/m (176), and there are two kinds of cation sites (4f and 6h) in the host lattice to accommodate the doping ions. The emissions of Eu2+ and Ce3+ at different lattice sites in the CPOCl host have been identified and discussed. The red shifted emission of CPOCl:Ce3+ with increasing Ce3+ doping concentrations has been explained, which is mainly attributed to the occupation of 6h sites of Ce3+ ions at a high doping level. In addition, the transformation from chlorapatite structures to oxyapatite structures driven by charge balance with Ce3+ concentrations also contributes to this red shift. When codoping Tb3+/Mn2+ ions into these cation sites, efficient energy transfers from Ce3+/Eu2+ ions to Tb3+/Mn2+ ions were observed, and the corresponding energy transfer mechanisms have been revealed. Under 340–420 nm near-ultraviolet light (n-UV) excitation, highly efficient blue-green tunable emission from Ce3+/Eu2+ ions to Tb3+ ions and single-phase white emission from Ce3+, Mn2+-codoped CPOCl can be obtained. In addition, the thermal stability of CPOCl:Ce3+/Eu2+,Tb3+/Mn2+ phosphors has been investigated systematically. Based on these experimental results, the as-prepared CPOCl:Ce3+/Eu2+,Tb3+/Mn2+ phosphors can act as potential color-tunable and single-phase white emission phosphors for possible applications in n-UV based white LEDs.

By cosubstituting [Ca2+–P5+] for [La3+–Si4+] in the Eu-doped Ca(2→8)La(8→2)(SiO4)6−x(PO4)xO2 (0 ≤ x ≤ 6) system, Eu3+ ions are controllably and gradually transformed to Eu2+. Thus, the emission colors consecutively changed from red to blue/green light. Furthermore, excellent warm-white lights with the low correlated color temperature (CCT) range of 3500–3800 K and a high color rendering index (Ra) (88.4–93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.

Here we report a novel Ca10(PO4)6O:Ce3+ phosphate phosphor, consisting of an apatite structure, whose emission peaks under excitation with near-ultra violet light were found to shift from 410 nm (blue light) to 510 nm (yellowish-green light) with an increasing Ce3+ doping level due to the Ce3+ at the different concentrations preferentially occupying different crystallographic sites.

In this paper, we present new insight into a changing Eu2+ crystallographic site preference in Eu-doped M5(Si3O9)2 (M = Sr, Ba, Y, Mn), which is related to the structural variation induced by M cation substitutions. The effect of the local structural geometry on the luminescence properties of Eu2+ is revealed. By substitution of Ba2+ for Sr2+, the lattice expansion is restricted to specific cation sites, resulting in the abrupt blue shifted emission of Eu2+ ions. The abnormal blue shift on replacing Sr2+ with Mn2+ is attributed to the preferential 6-fold coordination for Mn2+ that moves the Eu2+ ions to other sites. The results elucidate the mechanisms of emission band adjustment by local site coordination change and it can be potentially extended to crystals which properties are sensitive to local lattice variations.

Nowadays, phosphor converted white light-emitting diodes (pc-WLEDs) have been widely used in solid-state lighting and display areas due to their superior lifetime, efficiency, and reliability as well as significant reduction in power consumption. Phosphors are indispensable components of pc-WLED devices, and their luminescence properties determine the quality of WLED lighting and displays. In order to further achieve high luminous efficacy, chromatic stability, and color-rending properties in pc-WLEDs, much effort has been focused on improving current pc-WLED phosphors and developing novel pc-WLED phosphors recently. This review article concerns commonly used rare earth ion (Eu2+ and Ce3+) activated inorganic phosphors, highlighting the important effect of spectral tuning via local structural variations on improving the luminescence performance of phosphors. The main spectral tuning strategies are discussed in detail and summarized, including (1) doping level control; (2) cationic substitution; (3) anionic substitution; (4) cationic–anionic substitution; (5) the crystal-site engineering approach; (6) mixing of nanophases.

Uniform and monodisperse Gd(OH)3:Eu3+ hexagonal prisms were successfully synthesized at mild conditions via a large-scale and facile homogeneous coprecipitation process without using any catalysts, surfactants or templates. The size of the as-formed Gd(OH)3:Eu3+ precursor prisms could be modulated from the micro- to nanoscale by the use of urea and changing the pH values of the initial solutions. A possible formation mechanism for the Gd(OH)3:Eu3+ hexagonal nano-/microprisms was proposed. After a postannealing process, Gd2O3:Eu3+ hexagonal nano-/microprism phosphors with a slight shrinking in size can be transformed from Gd(OH)3:Eu3+. Both the Gd2O3:Eu3+ nanoprisms and microprisms exhibit the same strong red emission corresponding to the 5D0 → 7F2 transition (610 nm) of Eu3+ under UV light excitation (243 nm) and low-voltage electron beam excitation (1–6 kV). Furthermore, the experimental results indicate that the luminescence properties of the as-obtained phosphors are dependent on their morphologies and sizes. As a result of the controllable morphology and size, and excellent luminescence properties, these Gd2O3:Eu3+ nano-/microprism phosphors may find potential applications in optoelectronic devices (fluorescent lamps and field emission displays), bioanalysis and biomedical areas and so on.

A series of highly efficient and emission-tunable Sr3Y2(Si3O9)2(SYSO):Ce3+,Tb3+/Mn2+/Eu2+ phosphors have been prepared via a solid-state reaction. The structure refinement indicates that the as-prepared phosphors crystallized in a monoclinic phase with a space group of C2/c (no. 15), and there are three kinds of cation sites in the host lattice for the doped ions to occupy. The Ce3+ emission at different lattice sites in the SYSO host has been firstly identified and discussed. When introducing other doping ions into these cation sites, there exist efficient energy transfers from Ce3+ ions to these doping ions (Tb3+, Mn2+, and Eu2+) under UV excitation. The corresponding energy transfer mechanisms from Ce3+ to Tb3+/Mn2+/Eu2+ in SYSO:Ce3+,Tb3+/Mn2+/Eu2+ systems have been studied systematically. These energy transfers not only can enhance the luminescent efficiencies and broaden the width of emission spectra of SYSO:Ce3+,Tb3+/Mn2+/Eu2+ phosphors but also can modulate their emission colors from blue to green, orange or cyan, respectively. For example, the maximum quantum yields (QYs) of as-prepared SYSO:0.15Ce3+,xTb3+/yMn2+ phosphors can reach 90.4% and 74% at x = 0.70, y = 0.01, respectively. Based on these experiment results, the as-prepared SYSO:Ce3+,Tb3+/Mn2+/Eu2+ phosphors can act as potential color-tunable and emission band-widened phosphors for possible applications in ultraviolet light based white LEDs.

•Li2SrGeO4:Ce3+/Tb3+/Dy3+ phosphors were synthesized by a solid-state reaction.•Li2SrGeO4:Tb3+/Dy3+ phosphors show green and yellow emissions respectively.•Ce3+ enhances the luminescence intensity of Tb3+/Dy3+ through energy transfer.•The energy transfer mechanism is demonstrated to be a dipole–quadrupole interaction.Li2SrGeO4:RE3+ (RE = Tb/Dy/Ce) phosphors were prepared by the conventional solid-state reaction. X-ray diffraction (XRD), photoluminescence (PL) spectra, and lifetimes were utilized to characterize samples. Under the excitation of ultraviolet (231 nm for Tb3+ and 351 nm for Dy3+), the Li2SrGeO4:Tb3+ and Li2SrGeO4:Dy3+ phosphors show their respective characteristic emissions of Tb3+ (5D3,4 → 7FJ′, J′ = 3, 4, 5, 6) and Dy3+ (4F9/2 → 6H15/2 and 4F9/2 → 6H13/2), respectively. Ce3+ activated Li2SrGeO4 phosphors exhibit broad band blue emission due to the 5d–4f transition of Ce3+. Co-doping Ce3+ into the LSG: Ce3+/Dy3+ samples enhances the luminescence intensity of Tb3+ and Dy3+ significantly under the excitation wavelength at 340 nm through energy transfer from Ce3+ to Tb3+/Dy3+. In addition, the energy transfer mechanism between Ce3+ and Tb3+/Dy3+ has been demonstrated to be a resonant type via a dipole–quadrupole interaction.Graphical abstract

A series of Ca5(PO4)3Cl (CPOCl):Ce3+/Eu2+,Tb3+/Mn2+ phosphors with apatite structures have been prepared via the Pechini sol–gel process. The structure refinement indicates that the as-prepared phosphors crystallized in a hexagonal phase with the space group of P63/m (176), and there are two kinds of cation sites (4f and 6h) in the host lattice to accommodate the doping ions. The emissions of Eu2+ and Ce3+ at different lattice sites in the CPOCl host have been identified and discussed. The red shifted emission of CPOCl:Ce3+ with increasing Ce3+ doping concentrations has been explained, which is mainly attributed to the occupation of 6h sites of Ce3+ ions at a high doping level. In addition, the transformation from chlorapatite structures to oxyapatite structures driven by charge balance with Ce3+ concentrations also contributes to this red shift. When codoping Tb3+/Mn2+ ions into these cation sites, efficient energy transfers from Ce3+/Eu2+ ions to Tb3+/Mn2+ ions were observed, and the corresponding energy transfer mechanisms have been revealed. Under 340–420 nm near-ultraviolet light (n-UV) excitation, highly efficient blue-green tunable emission from Ce3+/Eu2+ ions to Tb3+ ions and single-phase white emission from Ce3+, Mn2+-codoped CPOCl can be obtained. In addition, the thermal stability of CPOCl:Ce3+/Eu2+,Tb3+/Mn2+ phosphors has been investigated systematically. Based on these experimental results, the as-prepared CPOCl:Ce3+/Eu2+,Tb3+/Mn2+ phosphors can act as potential color-tunable and single-phase white emission phosphors for possible applications in n-UV based white LEDs.

Here we report a novel Ca10(PO4)6O:Ce3+ phosphate phosphor, consisting of an apatite structure, whose emission peaks under excitation with near-ultra violet light were found to shift from 410 nm (blue light) to 510 nm (yellowish-green light) with an increasing Ce3+ doping level due to the Ce3+ at the different concentrations preferentially occupying different crystallographic sites.

By cosubstituting [Ca2+–P5+] for [La3+–Si4+] in the Eu-doped Ca(2→8)La(8→2)(SiO4)6−x(PO4)xO2 (0 ≤ x ≤ 6) system, Eu3+ ions are controllably and gradually transformed to Eu2+. Thus, the emission colors consecutively changed from red to blue/green light. Furthermore, excellent warm-white lights with the low correlated color temperature (CCT) range of 3500–3800 K and a high color rendering index (Ra) (88.4–93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.

Nowadays, phosphor converted white light-emitting diodes (pc-WLEDs) have been widely used in solid-state lighting and display areas due to their superior lifetime, efficiency, and reliability as well as significant reduction in power consumption. Phosphors are indispensable components of pc-WLED devices, and their luminescence properties determine the quality of WLED lighting and displays. In order to further achieve high luminous efficacy, chromatic stability, and color-rending properties in pc-WLEDs, much effort has been focused on improving current pc-WLED phosphors and developing novel pc-WLED phosphors recently. This review article concerns commonly used rare earth ion (Eu2+ and Ce3+) activated inorganic phosphors, highlighting the important effect of spectral tuning via local structural variations on improving the luminescence performance of phosphors. The main spectral tuning strategies are discussed in detail and summarized, including (1) doping level control; (2) cationic substitution; (3) anionic substitution; (4) cationic–anionic substitution; (5) the crystal-site engineering approach; (6) mixing of nanophases.