•The triple energy transfer of Gd3+→Tb3+, Gd3+→Eu3+, and Tb3+→Eu3+ in Sr3Gd(1-m-n)Na(PO4)3F:mTb3+,nEu3+ phosphors have been validated.•The emission colors can be varied from yellowish-green through yellow and eventually to reddish-orange by properly tuning the doping content of Eu3+.A family of apatite-type fluorophosphate phosphors with general formula Sr3Gd(1-m-n)Na(PO4)3F:mTb3+,nEu3+ (SGN:mTb3+,nEu3+) have been synthesized via the high-temperature solid-state reaction method. Triple energy transfer processes from Gd3+ in the host to both Tb3+ and Eu3+, as well as from Tb3+ to Eu3+ have been verified by the photoluminescence spectra. Under the excitation of UV light, both green line from the transitions of Tb3+ and red line origin from the transitions of Eu3+ have been simultaneously observed in a single phase phosphor, which makes a promise for tunable color emissions from yellowish-green through yellow and ultimately to reddish-orange by simply adjusting the Eu3+ content (n) in SGN:0.20Tb3+,nEu3+ phosphors. Additionally, the energy transfer from the Tb3+ to the Eu3+ ions has been demonstrated to be a resonant type via a quadrupole–quadrupole mechanism based on the Dexter's theoretical model, and the energy transfer efficiency increases with an increase in Eu3+ concentration.The triple energy transfer phenomenon of Gd3+→Tb3+, Gd3+→Eu3+, and Tb3+→Eu3+ in Sr3Gd(1-m-n)Na(PO4)3F:mTb3+,nEu3+ phosphors have been validated.Download high-res image (236KB)Download full-size image

Novel single-phased Eu2+/Mn2+-coactivated whitlockite-type Ca9MgK(PO4)7 phosphors which can emit white light upon UV light excitation, are prepared by the solid-state method, and their luminescence properties are systematically investigated via a combination of X-ray powder diffraction and spectroscopy measurements. For Eu2+–Mn2+ codoped samples, an efficient energy transfer process can takes place and its mechanism is a resonant type via a dipole-quadrupole interaction which can be elucidated by Dexter׳s theoretical model. Following the principle of energy transfer, myriad luminescence colors with a large gamut from blue to purplish red and across white zone in a line in the chromaticity diagram of the CIE can be obtained by simply adjusting the concentration ratio of Eu2+ to Mn2+. Photoluminescence spectra reveal that the white color emission is originated from the combination of two emission bands of Eu2+ and Mn2+ ions. Additionally, their CIE chromaticity coordinates and correlated color temperatures (CCT) have been calculated and discussed in detail. The luminescence suggest that whitlockite-type phosphor, Ca9MgK(PO4)7, co-activated with europium and manganese, is a promising single-phased white-emitting candidate for use in ultraviolet-chip-based white LEDs.

Eulytite-type orthophosphate phosphors Ba3Y(PO4)3:Eu2+, Mn2+ and Ba3Ln(PO4)3:Eu2+ (Ln = Lu, Y and Gd) were synthesized by high-temperature solid state reactions under reductive atmospheres. Their photoluminescence showed a surprising red-shift in the emission spectrum with the increase in the ionic radius of Ln in the Ba3Ln(PO4)3:Eu2+ (Ln = Lu, Y and Gd) phosphors system, which arises from the splitting of the 5d energy level. The phase formation, luminescence properties, and energy-transfer mechanism from the Eu2+ to the Mn2+ ions, and the CIE coordinates in the Ba3Y(PO4)3:Eu2+, Mn2+ phosphors were investigated. From powder X-ray diffraction (XRD) analysis, the formation of the single-phased Ba3Y(PO4)3 in a cubic crystal system with the space group I3d (no. 220) was confirmed. With the doping of Mn2+, the spectral overlap between the emission spectrum of Eu2+ and the excitation spectrum of Mn2+ allows resonance-type energy transfer to occur from Eu2+ to Mn2+ with the mechanism carefully studied by luminescence spectra, energy transfer efficiency and decay times. By increasing the Mn2+ doping concentration in the Ba3Y(PO4)3:Eu2+, Mn2+ phosphors, the emission colors can be tuned from yellowish-green through yellow and ultimately to orange. Such color tuning emissions originate from the change in intensity between the 4f–5d transitions of the Eu2+ ions and the 4T1–6A1 transitions of the Mn2+ ions through the energy transfer from the Eu2+ to the Mn2+ ions. In particular, compared with the commercial YAG:Ce phosphor, our developed phosphor contains a larger amount of red-emitting component; thus, it possesses favorable properties for application in warm white LEDs.