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Eu3+-activated La2CaB10O19 phosphors with nominal chemical formulae La2−xEuxCaB10O19 and La2Ca1−2xEuxNaxB10O19 were prepared. The luminescence properties under VUV-UV excitation were investigated. Luminescence spectra reveal Eu3+ ions occupy both Ca2+ and La3+ sites in all samples. The O2−→ Eu3+ charge transfer bands (CTBs) and the 5D0→7F0 emissions of Eu3+ at Ca 2+ site and La3+ site are identified, respectively. The schematic energy levels for Eu3+ in two sites were achieved. Luminescence decays of the 5D0→7F0 transitions were measured for both sites. [ABSTRACT FROM AUTHOR]

Eu3+-activated La2CaB10O19 phosphors with nominal chemical formulae La2−xEuxCaB10O19 and La2Ca1−2xEuxNaxB10O19 were prepared. The luminescence properties under VUV-UV excitation were investigated. Luminescence spectra reveal Eu3+ ions occupy both Ca2+ and La3+ sites in all samples. The O2−→ Eu3+ charge transfer bands (CTBs) and the 5D0→7F0 emissions of Eu3+ at Ca 2+ site and La3+ site are identified, respectively. The schematic energy levels for Eu3+ in two sites were achieved. Luminescence decays of the 5D0→7F0 transitions were measured for both sites. [ABSTRACT FROM AUTHOR]

Abstract: This report presents the luminescence properties of Ce3+ and Pr3+ activated Sr2Mg(BO3)2 under VUV–UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46729, 44643, 41667, 38314 and 29762cm−1 (i.e. 214, 224, 240, 261 and 336nm) for Ce3+ in the host lattice. The doublet Ce3+ 5d→4f emission bands were found at about 25840 and 24096cm−1 (387 and 415nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce3+ in Sr2Mg(BO3)2 were investigated. For Pr3+ doped samples, the lowest 5d excitation band was observed at about 42017cm−1 (238nm), a dominant band at around 35714cm−1 (280nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce3+ and Pr3+ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100photons/MeV of absorbed X-ray energy for the samples Sr1.86Ce0.07Na0.07Mg(BO3)2 and Sr1.82Pr0.09Na0.09Mg(BO3)2 at RT, respectively. [ABSTRACT FROM AUTHOR]

The phosphors, fluorapatites M5(PO4)3F (M=Ca, Sr, Ba) activated with Dy3+ ions, were prepared by a high-temperature solid-state reaction technique. The VUV-UV excitation spectra and emission spectra under VUV/UV excitation were measured. The phosphors show broad and strong absorption near 172 nm and intensive emission with the chromaticity coordinates entering the white light region. Hence, the phosphors may be considered as suitable candidates for Hg-free lamps. [ABSTRACT FROM AUTHOR]

Abstract: The spectroscopic properties of Na3Gd(PO4)2 and Na3Gd(PO4)2:Ce3+ phosphors in the VUV–UV spectral range were investigated. Five excitation bands of Ce3+ ions at Gd3+ sites are observed at wavelengths of 205, 246, 260, 292, and 321nm. Doublet Ce3+ 5d→4f emission bands are observed at 341 and 365nm with a decay constant τ 1/ e around 26ns. The X-ray excited luminescence of Na3Gd0.99Ce0.01(PO4)2 at room temperature shows a photon yield of ∼17,000photons/MeV of absorbed X-ray energy. [ABSTRACT FROM AUTHOR]

Abstract: The phosphors NaGdFPO4:Ln 3+ and GdPO4:Ln 3+ (for Ln3+=Ce3+ and Tb3+) were prepared by solid-state reaction technique, the VUV–vis spectroscopic properties of the phosphors were investigated, and we vividly compare the luminescence of Ce3+ and Tb3+ in the hosts. For phosphors GdPO4:Ln 3+, the band near 155nm in VUV excitation spectrum is assumed to be the host-related absorption, and for NaGdFPO4:Ln 3+ the absorption is moved to longer wavelength, near 170nm, showing the P–O bond covalency increased after fluoridation. The f–d transitions of Ce3+ and Tb3+ in the host lattices are assigned and corroborated, and it was found that the 5d states are with lower energy in NaGdFPO4:Ln 3+ than those in GdPO4:Ln 3+. For fluoridation of GdPO4:Ln 3+ to NaGdFPO4:Ln 3+, the energy change of Ln 3+ (Ln=Ce, Tb) 5d states is consistent with that of host-related absorption. [Copyright &y& Elsevier]

Abstract: The spectroscopic properties of Ce3+, Pr3+ and Tb3+ activated SrB4O7 in VUV–vis range were investigated. The split 5d levels for Ce3+ in the host lattice are discussed and an environmental factor F c is used to explain the crystal field splitting (CFS). The photon cascade emission (PCE) process was observed in Pr3+ doped SrB4O7, and the quantum efficiency of PCE is estimated. An empirical relationship between the lowest spin-allowed f–d transition energy [W fd(n)] and n-value for 4f n -series Ln3+ (Ln=Ce, Pr, Tb) ions in SrB4O7 is proposed. [Copyright &y& Elsevier]

In this work, a hybrid structure of multilayer transition-metal dichalcogenides (TMDs) and a ferroelectric polymer is designed to achieve passive control of optical properties in situ. The electrical polarization in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer can regulate the photoluminescence (PL) in bilayer WSe 2 . The total PL emission intensity is substantially suppressed or enhanced under large gate voltage in bilayer WSe 2 . This is because electrons transfer between the conduction band K valley and the conduction band Λ valley by the electrostatic field in the P(VDF-TrFE) polymer. This electron transfer further adjusts the proportion of direct and indirect excitons and, in turn, changes the overall optical radiation efficiency. We also illustrate that the engineered PL originates from the external electric-field-dependent transferred electron effect. The theoretical result matches the experimental data well. This work demonstrates a device platform in which passive regulation is achieved using 2D TMDs modulated by polarized ferroelectric materials.

Atomically thin layers of transition metal dichalcogenides (TMDs) have recently drawn great attention. However, doping strategies and controlled synthesis for wafer-scale TMDs are still in their early stages, greatly hindering the construction of devices and further basic studies. In this work, we develop the fast deposition of wafer-scale layered lanthanide ion Yb/Er co-doped WSe2 using pulsed laser deposition. WSe2 nanosheets were chosen as the host, while Yb3+ and Er3+ ions served as the sensitizer and activator, respectively. The obtained Yb/Er co-doped WSe2 layers exhibit good uniformity and high crystallinity with highly textured features. Under the excitation of a diode laser at 980 nm, down-conversion emission is observed at around 1540 nm, assigned to the emission transition between the 4I13/2 and 4I15/2 states of Er3+. Considering the significance of 1540 nm luminescence in the application of photonic technologies, this observation in the WSe2:Yb/Er nanosheets down to the monolayer provides a new opportunity for developing photonic devices at the 2D limit. Our work not only offers a general method to prepare wafer-scale lanthanide doped TMDs, but also to widely modulate the luminescence of atomically layered TMDs by introducing lanthanide ions.

Near-infrared-to-near-infrared (NIR-to-NIR) anti-Stokes luminescence from Cr 3+ singly doped Ca 3 Ga 2 Ge 3 O 12 (CGGG) occurs under the excitation of an 808 nm diode laser. The anti-Stokes processes vary from one photon to two photon, depending on the Cr 3+ content (x) in Ca 3 Ga 2-x Cr x Ge 3 O 12 . The results suggest that phonon-assisted anti-Stokes excitation and cooperative energy transfer are involved in the observed upconversion (UC) processes of CGGG:Cr 3+ . The relevant Cr 3+ -doping-concentration-dependent NIR-to-NIR anti-Stokes luminescent mechanism, either one-photon or two-photon UC, is investigated. Such an observation on modulating the UC process via varying the doping concentration is helpful in broadening the understanding of UC phenomena.