In order to improve the quality of lighting and display devices based on InGaN blue chips, blue light excitable red phosphor is an essential component. Here, we prepared a series of efficient red emitting phosphors of Mg14Ge5O24 doped with different concentrations of Mn4+ based on a conventional solid-state reaction. Crystal structure, composition, morphology, and luminescence properties of samples were characterized by utilizing Rietveld refinement, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and PL quantum yields (QYs). Moreover, reflectance spectra, temperature-dependent photoluminescence behavior, and the fabricated WLEDs performances were studied in detail. An absolute photoluminescence quantum yield as high as 81% was obtained for the Mg14Ge5(1–0.2%)O24:0.2%Mn4+ phosphor with good thermal stability. The fabricated WLED with CCT = 2864 K and Ra = 80.6 was attained by combining the prepared red phosphor and YAG yellow phosphor with a blue LED chip, which was superior to the conventional YAG-type WLED. All the results indicate that Mg14Ge5O24:Mn4+ is a promising phosphor and widens the horizon for materials in WLED applications.

In order to get efficient phosphors used in WLEDs to cover the shortage of red emission, highly saturated rare-earth-free red phosphors MGe4O9:Mn4+ (M = Sr, Ba) have been successfully fabricated by a solid state method at 1100 °C. The crystal structure properties including the phase purity were analyzed by means of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Photoluminescence absolute quantum efficiencies as well as lifetimes were utilized to characterize samples. As for the photoluminescence properties, the excitation spectra of samples exhibit two broad absorption bands with peaks at about 300 nm and 430 nm, which could be excited by near-UV/blue LED excitation. The emission spectra exhibit sharp peaks ranging from 600 nm to 700 nm due to the 4Eg → 4A2g transition of Mn4+ ions. The optimal Mn4+ doping concentrations in both the SrGe4O9 and BaGe4O9 host are determined to be 0.5 mol%. The critical energy transfer distances of these phosphors are calculated to be about 19 Å, and the concentration quenching mechanism is proved to be the dipole–dipole interaction. With increasing temperature, the luminescence of MGe4O9:Mn4+ (M = Sr, Ba) phosphors gradually decreases and the BaGe4O9:Mn4+ sample with the quenching temperature (T0.5) of about 180 °C has better thermal stability than SrGe4O9:Mn4+ with T0.5 of about 100 °C. Based on a combination of a blue LED chip, YAG:Ce3+ and MGO:0.5%Mn4+ red phosphors, the warm WLED is fabricated to explore its possible application as a warm white light-emitting diode.

•GdY(MoO4)3:RE3+ (RE = Eu, Dy, Sm, Tb) phosphor were synthesized via a Pechini-type sol–gel process.•Under the excitation, the GdY(MoO4)3:RE3+ phosphors exhibit the characteristic RE3+ emission.•The concentration quenching is not observed in the GdY(MoO4)3:xEu3+ system.•The emission intensities maximize at x = 0.05, 0.03, and 0.18 for Dy3+, Sm3+, and Tb3+ in the host.•The PL colors of GdY(MoO4)3:0.01Tb3+, xEu3+ samples can be tuned from green to red.GdY(MoO4)3:RE3+ (RE = Eu, Dy, Sm, Tb) phosphor were synthesized via a Pechini-type sol–gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) and cathodoluminescence (CL) spectra, and decay lifetimes etc were utilized to characterize the resulting samples. After annealed at 800 °C for 4 h in air, pure GdY(MoO4)3 phase can form. When the calcination temperature is further increased to 1100 °C, the crystallinity and luminescence intensity reach the best in our experiments. Under UV light and low-voltage electron beam excitation, the GdY(MoO4)3:Eu3+, GdY(MoO4)3:Dy3+, GdY(MoO4)3:Sm3+ and GdY(MoO4)3:Tb3+ phosphors exhibit the characteristic emission of Eu3+ (5D0-7F2, red), Dy3+ (4F9/2–6H13/2, yellow), Sm3+ (4G5/2–6H7/2, orange) and Tb3+ (5D4–7F5, green) with a high color purity, respectively. The Eu3+ and Tb3+ co-doping phosphors are capable of showing color-tunable emissions in the visible region under single-wavelength excitation. The luminescence mechanism and concentration quenching effect were discussed in detail.

Ca8MgLu(PO4)7:Ce3+,Tb3+,Mn2+ (abbreviated as CMLP:Ce3+,Tb3+,Mn2+) phosphors were synthesized by a high-temperature solid-state method. X-ray diffraction (XRD), photoluminescence (PL) spectra, GSAS structural refinement, and absolute quantum yield and lifetimes were used to characterize the samples. Increasing the Ce3+ doping concentration in the CMLP host shifts the emission peak from 360 to 374 nm. Under UV excitation, the energy transfers (ETs) from Ce3+ to Tb3+ and from Ce3+ to Mn2+ in the CMLP host occurred mainly via a dipole–quadrupole mechanism, and the critical distances of the ion pairs (RC) were calculated by the quenching concentration method and spectral overlap method, respectively. The emission colors of the CMLP:Ce3+,Tb3+,Mn2+ samples could be adjusted from blue to green, and eventually to orange–red by the ET between Ce3+ and Tb3+/Mn2+. Moreover, a white light emission tunable over a wide range was obtained by precisely controlling the contents of Ce3+, Tb3+ and Mn2+. Temperature dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. Based on the good PL properties and varied hues of the CMLP host achieved by adjusting the doping concentration of the activators (Ce3+, Tb3+, Mn2+), CMLP might be promising as a host material for solid-state lighting and display fields.

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu3+ was detected in the range of 570–650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si4+–Ca2+ to replace Al3+–Y3+, which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu3+ to Eu2+. The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1–xAl1–xSixO4:Eu0.01 (x = 0–0.30) exhibit both green emission of Eu2+ (4f65d1–4f7, broadband around 503 nm) and red-orange emission of Eu3+ (5D0–7F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1–xAl1–xSixO4:Eu0.01 (x = 0–0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, which would expand the application of Eu. Furthermore, this investigation reveals the correlations of structure and property of luminescent materials, which would shed light on the development of novel phosphors suitable for lighting and display applications.Keywords: crystal-site engineering; phosphors; Rietveld refinement; structure and property; tunable emission; WLEDs

•The novel garnet-based phosphors were synthesized by solid state reaction and investigated the luminescent properties.•The311/122-YAMSO:Ce3 +, Mn2 + phosphors exhibit a blue emission of Ce3 + ion and a orange-red emission of Mn2 + ion.•The emitting colors can be tuned from cool to warm white by adjusting the Mn2+ concentration through energy transfer.Presently considerable interest in single-phase white-emitting for ultraviolet light-emitting diodes is stimulated. Here we report the effective single-phase phosphors based on YAG-garnet structure, which exhibit varied hues from blue through white and eventually orange by tuning the relative proportion of Ce3 +/Mn2 + excited at ultraviolet.White-light generation and full-colors were obtained in single-phase garnet-based Y3Al5 − 2xMgxSixO12:Ce3 +, Mn2 + (Mg2 +–Si4 + replacing Al(1)3 +–Al(2)3 + in garnet-Y3Al5O12 host lattice on octahedron and tetrahedral sites, x = 1 and 2) phosphors using energy transfer principle.

Eu3+-/Er3+-activated YTiTaO6 phosphors have been prepared via conventional solid state reaction process. X-ray diffraction (XRD) and structure refinement, Raman spectra, X-ray photoelectron Spectrum (XPS), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and lifetimes were utilized to characterize the synthesized samples. Under UV light excitation, the YTiTaO6 sample shows broad band emission centered near 505 nm due to the Ta(Ti)O6 polyhedron. Eu3+ and Er3+ ions doped YTiTaO6 samples show strong line emissions coming from the characteristic f–f transitions. The energy transfer from the Ta(Ti)O6 group of the host to Eu3+ and Er3+ in YTiTaO6 phosphors has been demonstrated to be a resonant type via a dipole–dipole mechanism, and the critical distance (RC) for host emission to Eu3+ and Er3+ calculated by concentration quenching method are 10.02 and 18.86 Å, respectively. Under the low voltage electron beam excitation, the CL spectra of YTiTaO6, YTiTaO6: Eu3+, and YTiTaO6: Er3+ samples are similar to their PL spectra, exhibiting bluish-green, red, and green luminescence, respectively, which indicates that these materials might be promising for application in solid-state lighting and field-emission displays.

In order to improve the quality of lighting and display devices based on InGaN blue chips, blue light excitable red phosphor is an essential component. Here, we prepared a series of efficient red emitting phosphors of Mg14Ge5O24 doped with different concentrations of Mn4+ based on a conventional solid-state reaction. Crystal structure, composition, morphology, and luminescence properties of samples were characterized by utilizing Rietveld refinement, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and PL quantum yields (QYs). Moreover, reflectance spectra, temperature-dependent photoluminescence behavior, and the fabricated WLEDs performances were studied in detail. An absolute photoluminescence quantum yield as high as 81% was obtained for the Mg14Ge5(1–0.2%)O24:0.2%Mn4+ phosphor with good thermal stability. The fabricated WLED with CCT = 2864 K and Ra = 80.6 was attained by combining the prepared red phosphor and YAG yellow phosphor with a blue LED chip, which was superior to the conventional YAG-type WLED. All the results indicate that Mg14Ge5O24:Mn4+ is a promising phosphor and widens the horizon for materials in WLED applications.

In order to get efficient phosphors used in WLEDs to cover the shortage of red emission, highly saturated rare-earth-free red phosphors MGe4O9:Mn4+ (M = Sr, Ba) have been successfully fabricated by a solid state method at 1100 °C. The crystal structure properties including the phase purity were analyzed by means of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Photoluminescence absolute quantum efficiencies as well as lifetimes were utilized to characterize samples. As for the photoluminescence properties, the excitation spectra of samples exhibit two broad absorption bands with peaks at about 300 nm and 430 nm, which could be excited by near-UV/blue LED excitation. The emission spectra exhibit sharp peaks ranging from 600 nm to 700 nm due to the 4Eg → 4A2g transition of Mn4+ ions. The optimal Mn4+ doping concentrations in both the SrGe4O9 and BaGe4O9 host are determined to be 0.5 mol%. The critical energy transfer distances of these phosphors are calculated to be about 19 Å, and the concentration quenching mechanism is proved to be the dipole–dipole interaction. With increasing temperature, the luminescence of MGe4O9:Mn4+ (M = Sr, Ba) phosphors gradually decreases and the BaGe4O9:Mn4+ sample with the quenching temperature (T0.5) of about 180 °C has better thermal stability than SrGe4O9:Mn4+ with T0.5 of about 100 °C. Based on a combination of a blue LED chip, YAG:Ce3+ and MGO:0.5%Mn4+ red phosphors, the warm WLED is fabricated to explore its possible application as a warm white light-emitting diode.

Ca8MgLu(PO4)7:Ce3+,Tb3+,Mn2+ (abbreviated as CMLP:Ce3+,Tb3+,Mn2+) phosphors were synthesized by a high-temperature solid-state method. X-ray diffraction (XRD), photoluminescence (PL) spectra, GSAS structural refinement, and absolute quantum yield and lifetimes were used to characterize the samples. Increasing the Ce3+ doping concentration in the CMLP host shifts the emission peak from 360 to 374 nm. Under UV excitation, the energy transfers (ETs) from Ce3+ to Tb3+ and from Ce3+ to Mn2+ in the CMLP host occurred mainly via a dipole–quadrupole mechanism, and the critical distances of the ion pairs (RC) were calculated by the quenching concentration method and spectral overlap method, respectively. The emission colors of the CMLP:Ce3+,Tb3+,Mn2+ samples could be adjusted from blue to green, and eventually to orange–red by the ET between Ce3+ and Tb3+/Mn2+. Moreover, a white light emission tunable over a wide range was obtained by precisely controlling the contents of Ce3+, Tb3+ and Mn2+. Temperature dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. Based on the good PL properties and varied hues of the CMLP host achieved by adjusting the doping concentration of the activators (Ce3+, Tb3+, Mn2+), CMLP might be promising as a host material for solid-state lighting and display fields.