In previous decades, the global temperature has risen, and the saturation vapor pressure deficit (VPD) has increased. VPD is an important environmental factor affecting crops, especially their yields. However, the effects of various VPD conditions on water transport dynamics, anatomical structure, stomatal morphology, photosynthetic physiology, nutrient absorption, yield, and quality remain unclear. Many studies have shown that atmospheric transpiration is enhanced, water transport dynamics in the soil-plant-atmosphere continuum and water potential gradient are increased, and crop water potential is reduced under high VPD. Crops have undergone a series of changes that have enhanced their adaptation to high-VPD environments. Mesophyll thickness and conductance and stomatal size and conductance have decreased, and this has led to reductions in the photosynthetic rate and nutrient accumulation. High VPD seriously reduces the yield and water use efficiency of protected vegetables but improves fruit color and flavor quality. Reductions in VPD can improve water and nutrient transport in protected vegetables, alter the anatomical structure of crops, promote crop photosynthesis, and increase fruit yield, nutritional quality, and water use efficiency. Comprehensive analysis of the effect of VPD on the physiology and productivity of protected vegetables will provide insights that will aid the cultivation of protected vegetables with high quality and yield.

Er³⁺-sensitized upconversion nanoparticles (UCNPs) have attracted great attention due to their tunable upconversion (UC) emissions, low cytotoxicity, high resistance to photobleaching and especially multiple effective excitation wavelengths. However, detailed energy conversion between Er³⁺ and Tm³⁺ ions in Y₂O₃ UCNPs is still a problem, especially under multi-wavelength and variable pulse width excitation. In this work, we successfully fabricated a series of Er³⁺-sensitized Y₂O₃ nanocrystals by a spray flame synthesis method with a production rate of 40.5 g h⁻¹. The as-prepared UCNPs are a pure cubic phase with a mean size of 14 nm. Excited by both 980 and 808 nm lasers, the tunable upconversion luminescence (UCL) from Er³⁺ ions was achieved by increasing the Er³⁺ doping concentration, co-doping Tm³⁺ ions and extending excitation pulse-width. The investigations of the lifetimes and the laser power dependence of UC emissions further support the proposed mechanism, which provides guidance for achieving effective color control in anticounterfeiting and multiplexed labeling applications. In addition, the red UC emission at about 5 mm beneath the tissue surface was observed in an ex vivo imaging experiment under the excitation of 808 nm laser, indicating that the Y₂O₃:Er³⁺/Tm³⁺ UCNPs have great prospects in further biological applications.

Nd³⁺-sensitized nanoparticles have attracted attention recently due to their large absorption cross section and lower water absorption coefficient at 808 nm, which can potentially solve the laser-induced heating problem and is essential for labelling and imaging applications in living organisms. Here, we report a single-step hydrothermal synthesis of CaF₂:Yb³⁺/Er³⁺/Nd³⁺ upconversion nanoparticles (UCNPs). The size of the as-prepared UCNPs decreases from ∼138 to ∼30 nm as the Nd³⁺ doping concentration increases from 0 to 3 mol%. Under the excitation of a 808 nm continuous-wave (CW) laser, these UCNPs exhibit typical UC emissions at 539 nm (green) and 656 nm (red) for Er³⁺, and the luminescence is strongest when Nd³⁺ doping concentration is 0.75 mol%. Moreover, with the increase of doped Nd³⁺ ions, the suppressing of green and the enhancing of red UC emissions can be observed, which leads to the luminescence color tuning from green to red. Further investigations suggest that the resonant cross-relaxations (CRs) between Er³⁺ and Nd³⁺ ions contribute to the UC luminescence color changing and the remarkable red UC emission for the highly Nd³⁺-doped UCNPs. These advances make the UCNPs potentially to be applied in vivo labelling, bioimaging and phototherapy.

Although the diode pumped alkali laser (DPAL) works in a three-level scheme, higher energy-state excitation and ionization processes exist during operation, which may lead to deleterious effects on laser performance. In this paper, we report the ionization degree measurement in the gain medium of an operational hydrocarbon-free Rb DPAL by using the optogalvanic method. The results show that, at the pulsed mode with a duration of ~1 ms, a maximal ionization degree of ~0.06% is obtained at a pump power of 140 W. While in the CW mode, the plasma reaches an ionization degree as high as ~2% at a pump power of 110 W, which is mainly due to the enough time for sufficient plasma development. A comparison with our previous work [Opt. Lett. 39, 6501 (2014)] as well as modeling results is made and discussed. The influences of different population transfer channels on laser performance are simulated and analyzed. The results show that, for a typical hydrocarbon-free Rb laser (pump intensity of 15 kW/cm², helium pressure of 10 atm and cell temperature of 438 K), all the high-energy excitation effects give an overall negative influence on laser efficiency of ~3.78%, while the top two influencing channels are the photoionization (~1.8%) and the energy pooling (~1.53%). The work in this paper experimentally reveals the influence of the macroscopic ionization evolution process on an operational DPAL for the first time, which would be helpful for a more comprehensive understanding of the physics in DPALs.

The SARS-CoV-2 Omicron variant has become the dominant SARS-CoV-2 variant around the world and exhibits immune escape to current COVID-19 vaccines to some extent due to its numerous spike mutations. Here, we evaluated the immune responses to booster vaccination with intramuscular adenovirus-vectored vaccine (Ad5-nCoV), aerosolized Ad5-nCoV, a recombinant protein subunit vaccine (ZF2001) or homologous inactivated vaccine (CoronaVac) in those who received two doses of inactivated COVID-19 vaccines 6 months prior. We found that the Ad5-nCoV booster induced potent neutralizing activity against the wild-type virus and Omicron variant, while aerosolized Ad5-nCoV generated the greatest neutralizing antibody responses against the Omicron variant at day 28 after booster vaccination, at 14.1-fold that of CoronaVac, 5.6-fold that of ZF2001 and 2.0-fold that of intramuscular Ad5-nCoV. Similarly, the aerosolized Ad5-nCoV booster produced the greatest IFNγ T-cell response at day 14 after booster vaccination. The IFNγ T-cell response to aerosolized Ad5-nCoV was 12.8-fold for CoronaVac, 16.5-fold for ZF2001, and 5.0-fold for intramuscular Ad5-nCoV. Aerosolized Ad5-nCoV booster also produced the greatest spike-specific B cell response. Our findings suggest that inactivated vaccine recipients should consider adenovirus-vectored vaccine boosters in China and that aerosolized Ad5-nCoV may provide a more efficient alternative in response to the spread of the Omicron variant.

Size manipulation and red upconversion luminescence enhancement are simultaneously realized in CaF₂:Yb³⁺/Ho³⁺nanoparticles by doping with Ce³⁺ions.