Fluorescence enhancement of red and blue concurrently emitting Ba3MgSi2O8:Eu2+,Mn2+ phosphors for plant cultivation has been investigated by Dy3+ addition.The Ba3MgSi2O8:Eu2+,Mn2+,Dy3+(BMS-EMD) phosphors have two-color emissions at the wavelength peak values of 437 nm and 620 nm at the excitation of 350 nm.The two emission bands are coincident with the absorption spectrum for photosynthesis of plants.An obvious enhancement effect has been observed upon addition of Dy3+ with amount of 0.03 mol%,in which the intensities of both blue and red bands reach a maximum.The origin of red and blue emission bands is analysed.The photochromic parameters of the samples at the nearly UV excitation are tested.This fluoresence enhancement is of great significance for special solid state lighting equipment used in plant cultivation.
Europium-doped borosilicate glasses were prepared by melt-quenching procedure in the air.The mixed valence of Eu 2＋ and Eu 3＋ was identified by photoluminescence spectrum and electron paramagnetic resonance（EPR）.The existence of mixed valence was observed owing to the unequivalent substitution and de-polymerization network of the as-prepared borosilicate glasses.The variation of the glass composition in B 2 O 3 /BaO ratios changed the stability of the Eu 3＋ ions distinctly.In particular,as-prepared borosilicate glasses exhibited a tri-wavelength light excitable spectra centered at 397,466 and 534 nm to give the broadened orange-red emission at around 592 and 617 nm,due to supersensitive transitions of Eu 3＋ ions.This simultaneous tri-wavelength excitation happened to correspond with the emitting wavelength from near ultraviolet,blue AlInGaN chips and that from YAG：Ce 3＋.The total quantum yield（QY） of the Eu-doped glasses under 466 nm excitation was evaluated to be 10%,potentially providing a versatile combination with the europium-doped borosilicate glasses for red component addition to improve the quality of white light.
A method of color mixture for white light is presented with Sr3MgSi2O8:Eu2+, Mn2+ shell coated on Sr2SiO4:Eu2+ core by spray pyrolysis procedure. Upon near ultraviolet (NUV) excitation, a 550 nm band emission of Eu2+ from core host combines with the simultaneous emissions of Eu2+ at 457 nm and Mn2+ at 683 nm based on energy transfer in the shell lattice to generate warm white light with color rendering index (CRI) of 91. With such a core-shell-like structure, the re-absorption of blue light from shell layer can be effectively suppressed, and the chemical stability of the phosphor is verified experimentally to be superior to that of the Sr2SiO4:Eu2+. This new proposed phosphor provides great potential in the color mixture of blending-free phosphor converted white NUV light emitting diode (LED) devices.
The photoluminescence properties and energy transfer of a new Ce3＋/pr3＋/Eu3＋ co-doped solid-solution composi- tion of Sr2.975-xLaxAlO4＋xF1-x （LSAF） phosphor are investigated. Upon doping Pr3＋ into lattices of LSAF：Ce host, a shoulder emission peak is observed at about 620 nm, owing to the transition of 1D2 →3H4. Addition of Eu3＋ to LSAF：Ce3＋, Pr3＋ phosphor results in a sharp emission peaked at 675 nm for the 5D0 →TF3 transition and an increase of the intensity of red emission for Pr3＋ with increasing Eu3＋ concentration. The pathways of energy transfer among Ce3＋, Pr3＋, and Eu3＋ are proposed to be responsible for color addition of a red component to the primary yellow emission, enabling a potential adjustable color for blue excitable warm white.
We report a novel approach to obtaining a classical blue-green excitable CaS：Eu2＋ phosphor with desired red emission by microwave （MW） firing procedure in the absence of adding elemental sulphur. The disturbing effect of MW electro- magnetic field on decomposition of CaSO4 into CaS activated by europium is distinctly observed to give pure host phase without adding any elemental sulphur and carbon. The host phase evolution is observed to be highly dependent on the variation of applied MW power from X-ray diffraction （XRD） patterns and the corresponding photoluminescence （PL）, and a maximum PL intensity at 1100 W of MW power is acquired for the obtained purer host phase. The non-thermal and non-equilibrium effects by MW are revealed to correlate with the interaction between polar structure of the host and applied electromagnetic field. The results demonstrate an optional procedure to prepare this red-emitting phosphor in an effective, environment-friendly and scalable approach for phosphor production in the application of bio-illumination for plant cultivation and artificial photosynthesis.
The near-ultraviolet (n-UV) excited blue-emitting Sr2MgSi2O7:Eu2+ phosphors are used for fluorescence lamp and tricolor white LEDs. The effect of nitrogen-doped on the structure of the host and the enhancement of photoluminescence is experimentally investigated. The results show that as the amount of nitrogen-doped varies from 0 to 0.6 (at.), the luminous intensity is found to be increased to 169%, and the partial replacement of O by N results in a change of the crystal field by modifying the symmetry of the crystal structure. As a result, with the nitrogen-doped in small amount, the luminous intensity, chromaticity coordinates and the color purity can be adjusted to a desired value in the applications.
