Chunmeng Liu

A host sensitized reddish-orange Gd2MoO6:Sm3+ phosphor for light emitting diodes

An intense reddish-orange phosphor, Gd2MoO6:Sm3+, was developed by solid state chemistry. The photoluminescence excitation and emission spectra, concentration effect are investigated. The results show an efficient energy transfer from MoO66− group to Sm3+ occurs and Sm3+ ion emits an intense reddish-orange light with high color purity and an excellent reproduction quality of optical properties. These results demonstrate that Sm3+ ion with low 4f–4f absorption efficiency in near ultraviolet region can play a role of activator in narrow reddish-orange emitting phosphor potentially useful in ∼370 nm GaN-based light emitting diode through efficient energy feeding by charge transfer absorption of MoO66− group.

A high efficiency blue phosphor BaCa2MgSi2O8:Eu2+ under VUV and UV excitation

BaCa2MgSi2O8:Eu2+ phosphors have been prepared by a conventional high temperature solid state reaction technique. The emission and excitation spectra as well as the luminescence decays were investigated, showing that Eu2+ ions enter both Ba2+ and Ca2+ sites in the host. The structural refinement reveals that about 70% Eu2+ ions occupy Ba2+ sites in samples Ba1−xEuxCa2MgSi2O8 and BaCa2(1−x)Eu2xMgSi2O8. By investigation of the thermal-quenching, the schematic energy levels for Eu2+ in BaCa2MgSi2O8 were proposed. Intense blue emission was observed under 147, 172 and 254 nm excitation in comparison with the commercial blue phosphor BaMgAl10O17:Eu2+ (BAM), demonstrating the potential application of the phosphors in plasma display panels (PDPs) and tri-color fluorescent tubes.

UV-Vis-NIR luminescence properties and energy transfer mechanism of LiSrPO4:Eu2+, Pr3+ suitable for solar spectral convertor.

An efficient near-infrared (NIR) phosphor LiSrPO(4):Eu(2+), Pr(3+) is synthesized by solid-state reaction and systematically investigated using x-ray diffraction, diffuse reflection spectrum, photoluminescence spectra at room temperature and 3 K, and the decay curves. The UV-Vis-NIR energy transfer mechanism is proposed based on these results. The results demonstrate Eu(2+) can be an efficient sensitizer for harvesting UV photon and greatly enhancing the NIR emission of Pr(3+) between 960 and 1060 nm through efficient energy feeding by allowed 4f-5d absorption of Eu(2+) with high oscillator strength. Eu(2+)/Pr(3+) may be an efficient donor-acceptor pair as solar spectral converter for Si solar cells.

Luminescence and electronic properties of Ba2MgSi2O7:Eu2+: a combined experimental and hybrid density functional theory study

Photoluminescence properties of Ba2MgSi2O7:Eu2+ synthesized by a solid-state reaction method are first investigated in the vacuum ultraviolet (VUV) to visible (vis) excitation energy range. The band gap of the host is found to be around 7.44 eV. The incorporation of Eu2+ leads to bright green luminescence with weak thermal quenching above room temperature. Cathodoluminescence (CL) properties under low-voltage excitations are then studied, and the results suggest a potential application of the compound in field emission displays (FEDs). Electronic properties of the compound are finally calculated by a hybrid density functional theory (DFT) method, and are discussed in association with observed luminescence properties.

Enhanced emission of Mn2+ via Ce3+→Mn2+ energy transfer in α-Sr2P2O7

Mn(2+) doped and Ce(3+)-Mn(2+) co-doped α-Sr(2)P(2)O(7) phosphors were prepared by a traditional high-temperature solid-state reaction route. The UV-vis excitation and emission spectra for all samples were investigated. Luminescence of Mn(2+) is assigned to from two different sites, which is similar to that of Ce(3+). Energy transfer from Ce(3+) to Mn(2+) in co-doped phosphors α-Sr(2)P(2)O(7): 0.03Ce(3+), xMn(2+) and α-Sr(2)P(2)O(7): xCe(3+), 0.1Mn(2+) was investigated by the excitation and emission spectra as well as the luminescence decays. Both Ce(3+)(1) and Ce(3+)(2) can transfer energy to two types of Mn(2+) ions.

An intense charge transfer broadband sensitized near-infrared emitting CaLaGa 3 S 6 O:Yb 3+ phosphor suitable for solar spectral convertor

A near-infrared (NIR) phosphor, CaLaGa(3)S(6)O:Yb(3+), is developed as a promising solar spectral convertor for Si solar cells. The structure, photoluminescence excitation and emission spectra, concentration effect are investigated. The results show that CaLaGa(3)S(6)O:Yb(3+) has an efficient broad absorption band dominating around the 345 nm ascribing to the charge transfer state (CTS) of Yb(3+)-S(2-) and exhibits an intense NIR emission of Yb(3+) between 920 and 1150 nm, perfectly matching the maximum spectral response of Si solar cells. The NIR emission intensity of CaLaGa(3)S(6)O:Yb(3+) is 12 times as intense as that of a NIR quantum cutting phosphor Ca(2)BO(3)Cl:Ce(3+), Tb(3+), Yb(3+) (CBC) upon 4f-5d excitation of Ce(3+). These results demonstrate that the allowed CTS of Yb(3+)-S(2-) with high absorption cross-section can be an efficient and direct sensitizer harvesting UV-blue photons and greatly enhancing the NIR emission of Yb(3+) ion.

Host-sensitized luminescence of Dy3+ in LuNbO4 under ultraviolet light and low-voltage electron beam excitation: energy transfer and white emission

A series of LuNbO4:xDy3+ (x = 0–0.20) phosphors was prepared using a high-temperature solid-state reaction technique. X-ray diffraction (XRD) along with Rietveld refinement, field emission scanning electron microscopy (FE-SEM) observations, diffuse reflectance spectra (DRS), UV-vis photoluminescence (PL), fluorescence decays, PL quantum yields (QYs), and low-voltage cathodoluminescence (CL) were employed to characterize the phosphors. Nonradiative relaxation and host sensitization dramatically influence the LuNbO4:Dy3+ luminescence spectra and decay dynamics. It is shown that cross-relaxation arising from electric dipole–dipole interactions between adjacent Dy3+ ions is the leading mechanism of quenching the Dy3+ emission. The host sensitization for Dy3+ emission in LuNbO4 was confirmed and the energy transfer efficiency from the host to Dy3+ increased with increasing Dy3+ doping concentration/temperature. Upon excitation with ultraviolet light (261 nm) and a low-voltage electron beam (2 kV, 127 μA cm−2), the synthesized LuNbO4:Dy3+ phosphors show both the blue broadband emission of the LuNbO4 host and the characteristic emission of Dy3+ (the dominant one is the 4F9/2 → 6H13/2 transition, yellow), and the luminescence colour of the LuNbO4:Dy3+ phosphors can be tuned over a large gamut of colours by varying the Dy3+ doping concentration, and a single-phase intense white-light-emission has been achieved in the LuNbO4:0.015Dy3+ phosphor. On the basis of the good UV-vis PL and CL properties, LuNbO4:Dy3+ phosphors might be promising for applications in UV light-emitting diodes (UV-LEDs) and field emission displays (FEDs).

Optical Properties of Ce-Doped Li4SrCa(SiO4)2: A Combined Experimental and Theoretical Study

Investigation of optical properties of Ce3+-activated phosphors is not only of practical importance for various applications but also of fundamental importance for providing a basis to understand relevant properties of other lanthanide ions in the same host. We report herein a combined experimental and theoretical study of optical properties of Ce3+ in Li4SrCa(SiO4)2. Photoluminescence properties of the material prepared by a solid-state reaction method are investigated with excitation energies in the vacuum-ultraviolet (VUV) to ultraviolet (UV) range at low temperatures. The band maxima in the excitation spectra are assigned with respect to 4f → 5d transitions of Ce3+ at the Sr and Ca sites, from comparison between experimental and ab initio predicted transition energies. As a result of the two-site occupation, the material displays luminescence at 300-500 nm with a high thermal quenching temperature (>500 K), consistent with the calculated large gaps (∼1.40 eV) between the emitting 5d levels and the bottom of the host conduction band. On the basis of experimental and calculated results for Ce3+ in Li4SrCa(SiO4)2, the energy-level diagram for the 4f ground states and the lowest 5d states of all trivalent and divalent lanthanide ions at the Sr and Ca sites of the same host is constructed and discussed in association with experimental findings.

The Effect of Sr2+ on Luminescence of Ce3+-Doped (Ca,Sr)2Al2SiO7

A series of Ce3+-doped (Ca,Sr)2Al2SiO7 phosphors with different Ce3+ and Ca2+/Sr2+ concentrations were prepared by a high temperature solid-state reaction technique. To get insight into the structure-luminescence relationship, the impact of incorporation of Sr2+ on structure of (Ca,Sr)2Al2SiO7 was first investigated via Rietveld refinement of high quality X-ray diffraction (XRD) data, and then the VUV-UV excitation and UV-vis emission spectra of (Ca,Sr)2Al2SiO7:Ce3+ were collected at low temperature. The results reveal that the crystal structure evolution of (Ca,Sr)2Al2SiO7:Ce3+ has influences on band gaps and Ce3+ luminescence properties including 4f-5di (i = 1-5) transition energies, radiative lifetime, emission intensity, quantum efficiency, and thermal stability. Moreover, the influence of Sr2+ content on the energy of Eu3+-O2- charge-transfer states (CTS) in (Ca,Sr)2Al2SiO7:Eu3+ was studied in order to construct vacuum referred binding energy (VRBE) schemes with the aim to further understand the luminescence properties of (Ca,Sr)2Al2SiO7:Ce3+. Finally, X-ray excited luminescence (XEL) spectra were measured to evaluate the possibility of (Ca,Sr)2Al2SiO7:Ce3+ as a scintillation material.