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Additional file 1: Fig. S1. Variation of upconversion emission intensity as a function of Yb3+ dopant concentration when fixed the concentration of Ho3+ (0.1 mol%). Fig. S2. The UV–vis–NIR absorption spectra of SrF2:Yb3+/Ho3+ (12/0.1 mol%) NCs. Fig. S3. The dependence of luminescence intensity at (a) 1012 nm and (c) 2020 nm of SrF2:Yb3+/Ho3+ NCs on the temperature under 980 nm excitation. Arrhenius equation is used to fit the luminescence intensity dependent on temperature at (b) 1012 nm and (d) 2020 nm.

Harnessing the color tuning capability of upconversion nanoparticles (UCNPs) is of great significance in the field of advanced bioimaging and color display. Here, we report the tunable size and upconversion luminescence (UCL) multicolor in CaF2:Yb3+/Ho3+/Ce3+ UCNPs, which were synthesized by a facile hydrothermal method. It was found that the size of these UCNPs could be controlled (from 600 to 30 nm) by varying the concentration of Ce3+ ions. Under the excitation of a 980 nm continuous-wave (CW) laser, the UCL color of these UCNPs can be tuned from green to red as the doped Ce3+ ions gradually increase from 0 to 10 mol% and the red-to-green (R/G) ratio is enhanced remarkably. It is suggested that the cross-relaxation (CR) processes between Ho3+ and Ce3+ ions contribute to the tunable multicolor and enhancement of the R/G ratio. The mechanism of these processes is well supported by the time-resolved decay and near infrared (NIR) emission measurements.

The UC emission spectra, UCL intensity dependence on the pump power density and decay curves of UC emissions of the CaF2 UCNCs under multi-wavelength excitation.

How transplanted haematopoietic stem cells (HSCs) behave soon after they reside in a preconditioned host has not been studied due to technical limitations. Here, using single-cell RNA sequencing, we first obtained the transcriptome-based classifications of 28 haematopoietic cell types. We then applied them in conjunction with functional assays to track the dynamic changes of immunophenotypically purified HSCs in irradiated recipients within the first week after transplantation. Based on our transcriptional classifications, most homed HSCs in bone marrow and spleen became multipotent progenitors and, occasionally, some HSCs gave rise to megakaryocytic-erythroid or myeloid precursors. Parallel in vitro and in vivo functional experiments supported the paradigm of robust differentiation without substantial HSC expansion during the first week. Therefore, this study uncovers the previously inaccessible kinetics and fate choices of transplanted HSCs in myeloablated recipients at early stage, with implications for clinical applications of HSCs and other stem cells.

The alkali atom concentration plays an important role in the performance of a diode pumped alkali vapor laser (DPAL). At the rubidium DPAL operational region, the alkali concentration is as high as 1 0 13 − 1 0 14 c m − 3 , which is “optically thick,” or opaque, for the 780 nm or 795 nm doublet D lines when the traditional scanning absorption spectrum method is used for concentration measurement. To solve this problem, we propose the use of a probe laser of 420 nm, which corresponds to the 5 2 S 1 / 2 to 6 2 P 3 / 2 transition and has a lower absorption cross section compared to the D-line doublet. Due to the moderate absorption strength at a fixed 420 nm probe wavelength, we realized fast, online measurement of the Rb concentration in a real-world DPAL. By combining it with the quasi-two-level model, we further provided the population distribution in the lower three energy levels. This fast, online diagnostic method could be well applied in DPAL concentration measurement, and could show the dynamics of a laser’s performance.

The influence of spectrum characteristics on diode pumped alkali laser has been studied based on the rate equations. The result shows that, there exists an optimal operation temperature for alkali lasers, and the influences of temperature and gain medium length are equivalent, thus an efficiency, independent of temperature and length, can be introduced to describe the optimal efficiency when other parameters are fixed. The influence of pump linewidth on threshold pump intensity is linear, and a high efficiency may be achieved even when the pump linewidth is much broader than the atomic absorption linewidth because of the large absorption cross section in the far wings of alkali atoms. The influence of atomic absorption linewidth on threshold pump intensity is nonlinear, and as the absorpti

A Littrow external cavity was built to narrow the spectral linewidth of a diode laser to 0.16 nm by using a 2400 line/mm plane grating, with the center wavelength of the laser tunable. The laser was used as the pump source of the rubidium vapor laser. A chopper was employed to change the continuous laser to pulsed laser with the pulse width of 1 ms and the repetition rate of 100 Hz, then the laser was focused to a Rb vapor cell with the length of 8 mm which was filled with Methane at the pressure of 79 kPa. With the maximum peak power of the pulsed laser injected into the Rb cell is 1.84 W and the temperature of the cell is controlled at about 125 ℃, the linearly polarized fundamental mode Rb laser with the peak power of 17.5 mW is obtained.

The spectral linewidth of a 64-emitter laser-diode array is effectively suppressed by using a volume Bragg grating (VBG) based external cavity. At a maximal driven current of 90 A, the device produces a cw output of 80 W with 1.2 W/A slope efficiency and 0.1 nm spectral linewidth (FWHM) centered at 780nm. The power extraction efficiency reaches 90% as compared with the free running case. The central wavelength of the narrowed spectrum is tuned over a 0.3 nm range by adjusting the VBG's temperature. The absorption of 45% laser radiation by a 5-mm-long rubidium vapor cell with 150 Torr ethane and 450 Torr helium at 383 K is demonstrated.