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The phosphors Ca3(PO4)2:Tm3+ by co-doping Ce3+ have been synthesized by conventional high-temperature solid-state reaction method. Their spectroscopic properties in the UV-VIS-NIR range have been investigated. The first 5d crystal field level location and stokes shift have been determined from the UV excitation and emission spectra of Ca3(PO4)2:Ce3+. The three-photon NIR quantum-cutting luminescence of Tm3+ assigned to the electronic transitions of 1G4→3H4, 3H4→3F4 and 3F4→3H6 is observed, whether in Ca3(PO4)2:Tm3+ or Ca3(PO4)2:Tm3+,Ce3+. The energy transfer from Ce3+ to Tm3+ takes place with energy-transfer efficiency up to 34.5% for the Ca3(PO4)2:Tm3+,Ce3+. A cross relaxation scheme using the 5d states of Ce3+ and f-f transition of Tm3+ is proposed. The mechanism is revealed from energy level and decay measurements. The results show that the broadband absorption of Ce3+ sensitizer not only extends the spectrum conversion in UV region but also greatly enhances the photoluminescence intensities of the three-photon quantum cutting luminescence of Tm3+ doped Ca3(PO4)2. [ABSTRACT FROM AUTHOR]

An efficient three-photon near-infrared (NIR) quantum cutting (QC) is reported in Tm3+ singly doped YVO4 polycrystalline phosphors, where an optimized content of Tm3+ is determined to be 1.0 mol. %. Upon the absorption of a visible photon around 473 nm, three NIR photons emitting at 1180, 1479, and 1800 nm can be obtained efficiently by the sequential three-step radiative transitions of Tm3+. The underlying mechanisms are analyzed in terms of the steady and dynamic fluorescence spectra measurements. Internal quantum yield is calculated to be 161.8% as a theoretical value when luminescence quenching due to defect species can be overcome. In addition, the broadband ultraviolet (UV)-excited [VO4]3- can strongly sensitize the 1G4 level of Tm3+ in the wavelength range likely from 250 to 360 nm, greatly increasing the UV photo-response and NIR fluorescent intensity of Tm3+. The further development of this broadband three-photon NIR QC material would explore the new route to improve the photo-response of novel photoelectronic devices, particularly in 250-360 nm. [ABSTRACT FROM AUTHOR]