•Branching fractions (BFs) of Ba I for 108 lines were measured by a high-resolution grating spectrometer with a hollow-cathode lamp.•Corresponding transition probabilities and oscillator strengths were deduced by combining these BFs with the radiative lifetime data in literature.•The uncertainties for most BFs are less than 10%, except for some extremely weak lines.Branching fractions (BFs) of Ba I for 108 lines including 96 lines from 33 odd-parity levels with the configurations 5dnp (n = 6, 7, 8), 6snp (n = 7, 8, 11, 12), 6snf (n = 5, 6, 11, 16) and 5d4f, as well as 12 lines from 5 even-parity levels with the configurations 6snd (n=7, 9, 12) and 5d6d were measured using a high-resolution grating spectrometer with a hollow-cathode lamp. By combining the data of natural radiative lifetimes published in literature, the transition probabilities and oscillator strengths for these lines were also deduced, and the achieved results are in fair agreements with the previous ones.

•Hyperfine structure measurement of the 4s2nd 2D3/2 Rydberg sequence in Ga I.•Determination of the nuclear moment ratios between the two stable isotopes of Ga.•Measurement of radiative lifetimes of the 4s2nd 2D3/2 Rydberg sequence in Ga I.The hyperfine structure (HFS) constants of the 4s2nd 2D3/2 (n=6–18) Rydberg sequence and the 4s26p 2P3/2 level for two isotopes of 69Ga and 71Ga atoms were measured by means of the time-resolved laser-induced fluorescence (TR-LIF) technique and the quantum beat method. The observed hyperfine quantum beat spectra were analyzed and the magnetic-dipole HFS constants A as well as the electric-quadrupole HFS constants B of these levels were obtained by Fourier transform and a program for multiple regression analysis. Also using TR-LIF method radiative lifetimes of the above sequence states were determined at room temperature. The measured lifetime values range from 69 to 2279 ns with uncertainties no more than 10%. To our knowledge, the HFS constants of this Rydberg sequence and the lifetimes of the 4s2nd 2D3/2 (n=10–18) levels are reported for the first time. Good agreement between our results and the previous is achieved.

•The experimental lifetimes of some Mn I and Ni I levels were obtained by time-resolved laser induced fluorescence method.•Radiative lifetimes of 26 energy levels in Mn I were reported for the first time.•Radiative lifetimes of 9 energy levels in Ni I were reported for the first time.Natural radiative lifetimes for 32 excited levels of Mn I and for 17 excited levels of Ni I were measured using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy in laser-induced plasma. The energy regions are from 45,754.27 to 54,950.81 cm−1 for Mn I and from 28,578.018 to 50,851.199 cm−1 for Ni I. The uncertainties of all lifetime results are within 10%. To our best knowledge, 26 lifetime results of Mn I and 9 lifetime results of Ni I are reported for the first time.

•Eu3+-doped cubic Ba3Y2WO9 phosphors were firstly synthesized by sol–gel method.•The luminescence excitation and emission spectra were discussed in details.•The crystallographic occupations of Eu3+ ions in cubic Ba3Y2WO9 were explored.Eu3+-doped cubic double perovskite Ba3Y2WO9 phosphors have been firstly successfully synthesized by sol–gel method. The prepared samples were characterized by X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The luminescence excitation and emission spectra in the ultraviolet–visible (UV) region were used to investigate the luminescence properties of these phosphors. Then the site-selective excitation and emission spectroscopy along with luminescence decay have been investigated in the 5D0 → 7F0 region under a pulsed, tunable, narrowband dye laser at room temperature. In our study, the crystallographic occupations of Eu3+ ions were explored based on both spectroscopy and crystal structure of cubic Ba3Y2WO9:Eu3+. The multiple site structure of Eu3+ ions with highly disordered distributions in cubic Ba3Y2WO9 lattices was suggested. The results help us to understand the site assignments of rare earth ions doped in cubic Ba3Y2WO9.Graphical abstract

Cubic monodisperse BaCeF5 and BaCeF5:Tb3+ nanocrystals have been successfully synthesized by a citric acid assisted solvothermal method. The crystalline phase, size, morphology, and luminescence properties were characterized using powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescent excitation spectra (PLE) as well as dynamics decay. The results reveal that the Tb3+-doped BaCeF5 sample shows a strong green emission centered at 546 nm, corresponding to the 5D4→7F5 transition of Tb3+ due to an efficient energy transfer from Ce3+ to Tb3+. The decay lifetime of Ce3+ monotonically increases with increase of Tb3+ concentration. The critical energy transfer distance between Ce3+ and Tb3+ was also calculated by methods of concentration quenching and spectral overlapping. Experimental analysis and theoretical calculations reveal that the dipole–dipole interaction should be the dominant mechanism for the Ce3+–Tb3+ energy transfer.

Photoluminescence properties of Eu3+-doped GdAlO3 and LaAlO3 phosphors prepared by sol–gel method have been investigated by the site-selective laser spectroscopy along with the decay time measurements at room temperature. The site-selective excitation spectra showed one 7 F0 → 5D0 transition line in GdAlO3:Eu3+ and three 7 F0 → 5D0 transition lines in LaAlO3:Eu3+, indicating that there was only one crystallographic site for Eu3+ in GdAlO3 and three crystallographic sites for Eu3+ in LaAlO3. The result of LaAlO3 was not in agreement with its crystal structure. The stark energy levels for Eu3+ at different sites were characterized and discussed by site-selective emission spectra arose from 5D0 level of Eu3+.Highlights► The site-selective laser spectroscopy of Eu3+:RAlO3 (R = Gd, La) were investigated. ► One crystallographic site in Eu3+:GdAlO3 is assigned. ► Three crystallographic sites in Eu3+:LaAlO3 are assigned. ► Decay times of 5D0 → 7 F2 emission of Eu3+:RAlO3 (R = Gd, La) were also measured.

Novel monodisperse BaCeF5 and BaCeF5: Tb3+, Sm3+ nanocrystals have been successfully synthesized by a simple one-step solvothermal synthesis. Uniformly distributed nanocrystals with an octahedral morphology and particle size of 75–80 nm were observed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and decay studies were employed to characterize the samples. Under ultraviolet irradiation, the BaCeF5: Tb3+, Sm3+ samples exhibit the typical green emission band of the Tb3+ ions, as well as an orange-red and red emission bands of the Sm3+ ions in the presence of Ce3+ ions. The highly intense orange-red and red emission bands of the Sm3+ ions were attributed to the effective energy transfer from the Tb3+ to Sm3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of BaCeF5: Tb3+, Sm3+ nanophosphors can be easily tuned by changing the concentration of Sm3+ ions. These results suggest that BaCeF5: Tb3+, Sm3+ nanocrystals can be explored for three-dimensional displays, back lighting, white light sources, and so on.

The sensitivities of UC mechanisms to exciting wavelength have been studied in Er3+:YAG crystals with 8.4 and 10.5 at.% dopant concentrations. The impacts of both the dopant concentration and the excitation wavelength on UC fluorescence have been taken into account together and it has been found that in samples with different concentrations though the UC fluorescence concerning the 2P3/2 and the 2G9/2 levels are obviously distinct, their sensitivities to exciting wavelength are very similar.Research highlights► Research on mechanism-competition extends to a stage with different concentrations. ► Influences of both doped concentration and exciting wavelength are considered. ► The UC fluorescence are obviously different in two samples. ► The sensitivities to exciting wavelength are similar with different concentrations.

A sensitive dependence of upconversion (UC) mechanisms on excitation wavelength in a rather small region of 0.5 nm near to the resonant absorption of 4F7/2 in Er3+(8.4 at%):YAG crystal has been observed and discussed. This kind of mechanism-sensitive UC luminescence comes from 2P3/2 which can be upconvertedly populated by both excited-stated absorption (ESA) and energy-transfer upconversion (ETU) processes. From a qualitative analysis, similar to the dependence of UC mechanisms on dopant concentration, the essence of this sensitivity reflects the influence of the interacting ion number on ETU. In order to give a quantitative description, we also performed a simulation for UC processes by rate equations, and the theoretical results attested the sensitivity as revealed in the experiment.

We experimentally report on the energy position, branching ratios, lifetimes and emission cross sections of the 1S0 level in Pr3+:ZBLAN glasses by two-step excitation process: 3H4 → 1D2 → 4f5d. The calculated branching ratios and lifetimes of 1S0 by the standard as well as the modified Judd-Ofelt theories are compared with the measured ones. The results by the modified Judd-Ofelt theory, which more reasonably takes into account the effects of the configuration energies on the 5d perturbations to the 4f levels, have better agreements with the experimental results. The 1S0 luminescence by another two-step excitation process 3H4 → 3P0 → 4f5d is also discussed.

The effects of activator concentration on the relaxation of the 1I6, 1D2, 1G4 and 3H4 levels of Tm3+ were investigated by the analysis of the fluorescence decay curves in Tm3+ and Tm3+/Tb3+ doped ZBLAN glasses. UV and blue upconversion luminescence bands around 362 and 450 nm were observed by 655 nm laser excitation in all the samples. The upconversion mechanism was attributed to excited state absorption (ESA) by analyzing the decay profiles and the intensity dependence.

Ultraviolet and visible upconversion properties of Er3+ in YAlO3 were investigated following 652.2 nm excitation of the multiples 4F9/2. The luminescence and excitation spectra were recorded. Ultraviolet (326–342 and 354–359 nm), violet (405–420 nm), blue (436–442 nm) and green (525–575 nm) upconversion and infrared downconversion luminescence were simultaneously observed. The intense green luminescence corresponds to the emissions from the thermal coupled 4S3/2 and 2H11/2 bands and 2G9/2 level. Energy transfer upconversion processes were proposed to explain the upconversion phenomena. The luminescence kinetics was discussed in detail by the analyses of fluorescence decay curves.

Oscillator strengths for 16 lines of Pd I from 4d95s–4d95p transitions have been derived by combining the adopted lifetimes with the data of branching fractions measured in this work based on the emission spectrum of a hollow cathode lamp. The results have some significant differences compared with the reported in the literature. Among them the results of 13 lines improves the reported data. New results obtained in this paper are useful for more accurate spectra analysis concerning Pd atom.

The lifetimes of 3P0 and 1D2 levels of Pr3+ were measured in ZBLAN glasses of composition in mol% 53ZrF4–20BaF2–(4 − x)LaF3–3AlF3–20NaF–xPrF3 (x = 0.1, 0.5, 1, and 3) by resonant excitation. Energy transfer observed between Pr3+ ions was analyzed by means of the Inokuti–Hirayama theory. The non-exponential dependence of the 1D2 decay on Pr3+ concentration indicates that dipole–dipole interaction between Pr3+ is the main process. Orange-to-blue upconversion luminescence was observed and described by two-ion energy transfer mechanism. The temporal evolution of upconversion luminescence was characterized by rise and decay times related to the dopant concentration.

A theoretical study for ultraviolet upconversion fiber master oscillator power amplifier (MOPA) based on the transition from the 4f5d state to the 3H4 ground state in Pr3+:ZBLAN fiber is performed by using steady population rate equations and propagation equations. The variation of the output power with the fiber length of master oscillator and MOPA and the launched pump powers, the dependence of the slope efficiency on the fiber length of master oscillator and MOPA, and the optimum fiber length of MOPA as a function of the launched pump powers, are calculated. Both the output power and the slope efficiency of MOPA are 2–3 times those of the simplex oscillator. It is found that the UV upconversion fiber MOPA system can effectively improve the output power and the slope efficiency of laser.