The enhanced responsivity and response speed of SnO2 visible-blind transparent photodetectors via the SiO2 passivation layer.

Recently, transparent ultraviolet (UV) photodetectors have gained wide attention for their giant potential in integrated transparent electronics applications. SnO2 films as a common candidate for visible-blind transparent ultraviolet photodetectors have attracted increasing attention. In this work, high-performance visible-blind transparent UV photodetectors based on SnO2 thin film and a SiO2 passivation layer were successfully synthesized by the sol-gel spin coating method for the first time. The obtained SnO2/SiO2 hybrid device has a transmittance of nearly 80% in the visible band at 400-700 nm and demonstrates a high responsivity of 769 mA W-1 and a detection sensitivity of 1.24 × 1014 Jones under UV light illumination. The UV-C/UV-A rejection ratio is greater than 106, indicating that the device has good photo-selectivity. In addition, after the introdution of the SiO2 layer, the response speed is 2 times higher than that of pure SnO2. The presence of the SiO2 layer reduces the exposed area of SnO2, passivates the oxygen vacancies on the surface of SnO2 and inhibits the surface chemical adsorption. The above results provide a new perspective for improving the performance of SnO2 thin film for visible-blind transparent ultraviolet photodetectors.

Aluminate Red Phosphor in Light-Emitting Diodes: Theoretical Calculations, Charge Varieties, and High-Pressure Luminescence Analysis.

Searching for a non-rare-earth-based oxide red-emitting phosphor is crucial for phosphor-converted light-emitting diodes (LEDs). In this study, we optimized a blue and UV-light excited Sr4Al14O25:Mn phosphor exhibiting red emission peaked at ∼653 nm, which was successfully synthesized by solid-state reaction. The crystal structure, micromorphology, and luminescent properties of Sr4Al14O25:Mn phosphors were characterized by X-ray Rietveld refinement, high-resolution transmission electron microscopy, and photoluminescence spectra. The band gap and electronic structure of Sr4Al14O25 were analyzed by density functional theory calculations using the hybrid exchange-correlation functional. The crystal field environment effect of Al sites from introducing activator Mn ions was investigated with the aid of Raman 27Al nuclear magnetic resonance spectra and electron spin resonance. The pressure dependent luminescent properties and decay time of this compound were presented. The tricolor display spectrum by combining blue InGaN chips, commercial ß-SiAlON:Eu2+ green phosphor, and Sr4Al14O25:Mn red phosphor were evaluated for commercial applications: using the present Sr4Al14O25:Mn red phosphor converted LED as a backlighting source.

Ab Initio Site Occupancy and Far-Red Emission of Mn4+ in Cubic-Phase La(MgTi)1/2O3 for Plant Cultivation.

Mn4+-activated oxide phosphors La(MgTi)1/2O3 (LMT) with far-red emitting were prepared via a sol-gel route. The structures of samples were determined by X-ray diffraction (XRD) and Reitveld refinement. The occupied sites of Mn4+ (d3 electronic configuration) in host La(MgTi)1/2O3 were confirmed by ab initio calculations in which the system has the lower formation energy, stable lattice structure, and strong bonding state as Mn4+ enters into Ti site. The luminescent properties of Mn4+-doped samples were investigated; the samples emit far-red light centered at 708 nm with ultraviolet light (345 nm) or blue light (487 nm) excitation. According to the photoluminescence (PL) and excitation (PLE) spectra, the crystal field strength of the Mn4+-occupied environment was estimated. The thermal stability of phosphor was also evaluated through temperature-dependent PL intensity in a heating and cooling cycle process. The emission band is well-matched with the absorption band of phytochrome PFR under the excitation of light in near-ultraviolet to blue, which suggests that the LMT: Mn4+ phosphor has great potential applications in light-emitting diodes (LEDs) for modulating plant growth.

Site-Dependent Luminescence and Thermal Stability of Eu(2+) Doped Fluorophosphate toward White LEDs for Plant Growth.

Eu(2+) activated fluorophosphate Ba3GdNa(PO4)3F (BGNPF) with blue and red double-color emitting samples were prepared via a solid-state method in a reductive atmosphere. Their crystal structure and cationic sites were identified in light of X-ray diffraction pattern Rietveld refinement. Three different Ba(2+) sites, coordinated by six O atoms referred to as Ba1, two F and five O atoms as Ba2, and two F and six O atoms as Ba3, were partially substituted by Eu(2+). Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor BGNPF:Eu(2+) along with the lifetimes were characterized at the liquid helium temperature (LHT), which further confirm the existence of three Eu(2+) emitting centers resulting in 436, 480, and 640 nm emission from the 5d → 4f transitions of Eu(2+) in three different Ba(2+) crystallographic sites. These emissions overlap with the absorption spectra of carotenoids and chlorophylls from plants, which could directly promote the photosynthesis. Temperature-dependent PL spectra were used to investigate the thermal stability of phosphor, which indicates that the PL intensity of BGNPF:0.9% Eu(2+) with optimal composition at 150 °C still keeps 60% of its PL intensity at room temperature, in which blue emission has higher thermal-stability than the red emission. Furthermore, the approaching white LED devices have also been manufactured with a 365 nm n-UV LED chip and present phosphor, which make operators more comfortable than that of the plant growth purple emitting LEDs system composed of blue and red light. Results indicate that this phosphor is an attractive dual-responsive candidate phosphor in the application n-UV light-excited white LEDs for plant growth.

Thermometry and up-conversion luminescence of Yb(3+)-Er(3+) co-doped Na2Ln2Ti3O10 (Ln = Gd, La) phosphors.

Yb(3+)/Er(3+)-ion co-doped Na2Ln2Ti3O10 (Ln = Gd, La) up-conversion (UC) phosphors were successfully synthesized by a sol-gel method, and their crystal structures were characterized by powder X-ray diffraction. Dazzling yellow-greenish light was emitted under the excitation of 980 nm near-infrared (NIR) light, composing green and red emission bands from the (2)H11/2/(4)S3/2→(4)I15/2 and (4)F9/2→(4)I15/2 transitions of Er(3+), respectively. The optimal composition and synthesis parameters were determined according to their UC emission intensity. The photon absorption and emission processes were illustrated based on the UC mechanism, in which energy transfer (ET) from Yb(3+) to Er(3+) plays a pivotal role and has been proved by the variation of green emission lifetime in Er(3+) singly and Yb(3+)/Er(3+) co-doped Na2Ln2Ti3O10 samples. The temperature-dependent fluorescence intensity ratios (FIR) of the two thermal coupled energy level (TCL) emission from (2)H11/2→(4)I15/2 (526 nm) and (4)S3/2→(4)I15/2 (549 nm) were calculated in the range of 290-490 K, and their sensitivity values were approximately 0.0058 K(-1) for Na2Gd2Ti3O10 at 490 K and 0.0061 K(-1) for Na2La2Ti3O10 at 470 K, as potential optical temperature sensor.

Color tunable emission in Ce3+ and Tb3+ co-doped Ba2Ln(BO3)2Cl (Ln=Gd and Y) phosphors for white light-emitting diodes.

Ce(3+) and Tb(3+) co-doped Ba2Ln(BO3)2Cl (Ln=Y and Gd) green emitting phosphors were prepared by solid state reaction in reductive atmosphere. The emission and excitation spectra as well as luminescence decays were investigated, showing the occurrence of efficient energy transfer from Ce(3+) to Tb(3+) in this system. The phosphors exhibit both a blue emission from Ce(3+) and a green emission from Tb(3+) under near ultraviolet light excitation with 325-375 nm wavelength. Emission colors of phosphors could be tuned from deep blue through cyan to green by adjusting the Tb(3+) concentrations. The energy transfer efficiency and emission intensity of Ba2Y(BO3)2Cl:Ce(3+), Tb(3+) precede those of Ba2Gd(BO3)2Cl:Ce(3+), Tb(3+), and the sample Ba2Y(BO3)2Cl:0.03Ce(3+), 0.10Tb(3+) is the best candidate for n-UV LEDs.