Luminescent properties of Ca2BO3Cl:Eu yellow-emitting phosphor for white light-emitting diodes

The Ca₂BO₃Cl:Eu²⁺ phosphor was synthesized by the general high temperature solid-state reaction and an efficient yellow emission under near-ultraviolet and blue excitation was observed. The emission spectrum shows a single intense broad emission band centered at 573 nm, which corresponds to the allowed f-d transition of Eu²⁺. The excitation spectrum is very broad extending from 350 to 500 nm, which is coupled well with the emission of UV LED (350-410 nm) and blue LED (450-470 nm). The measured emission of In-GaN-based Ca₂BO₃Cl:Eu²⁺ LED shows white light to the naked eye with a chromatic coordinate of (0.33, 0.36). The Ca₂BO₃Cl:Eu²⁺ is a very appropriate yellow-emitting phosphor for white LEDs.     

A novel green emitting phosphor Ca1.5Y1.5Al3.5Si1.5O12:Tb

Vacuum ultraviolet (VUV) excitation and emission properties of Tb³⁺ ion doped silico-aluminate phosphor Ca_1.5Y_1.5Al_3.5Si_1.5O₁₂:Tb³⁺ was studied. Upon excitation with vacuum ultraviolet (VUV) and near UV light excitation, the phosphor showed strong green-emission peaked at 545 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, and the highest PL intensity at 545 nm was found at a content of about 14 mol% Tb³⁺. The 4f–5d transition absorption of Tb³⁺ is in the range from 150 nm to 260 nm, and there is an energy transfer from the host to the rare earth ions. Field emission scanning electron microscopy (FE-SEM) images showed the particle size of the phosphor was less than 3 μm.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Oxygen-doped ZnTe phosphors for synchrotron X-ray imaging detectors

ZnTe:O powder phosphors were successfully prepared by a dry synthesis process using gaseous doping and etching media. It was found that dry doping by O₂ through ball-milling was an effective way to synthesize ZnTe:O powder phosphors and produced a red emission centered at 680 nm with a decay time of 1.1 μs. The emission intensity of dry O₂-doped samples was three times more intense than from ZnO-doped samples, possibly due to a more uniform distribution of oxygen substitution on tellurium sites. The samples annealed in a 95% N₂/5% H₂ forming gas atmosphere exhibited a x-ray luminescent efficiency five times higher than did powders annealed in vacuum or N₂ atmosphere. This enhancement was attributed to the removal of surface tellurium oxides. ZnTe:O phosphor screens were prepared with x-ray luminescence efficiencies equivalent to 56% of ZnSe:Cu,Ce,Cl and 76% of Gd₂O₂S:Tb screens under 17-keV radiation. An x-ray imaging resolution of 2.5 lines/mm was resolved, the same as that measured for commercial ZnSe:Cu,Ce,Cl and Gd₂O₂S:Tb screens. These results indicate that ZnTe:O is a promising phosphor candidate for synchrotron x-ray imaging applications.     

Low-temperature solid-state synthesis and luminescent performance of a novel Li2NaBP2O8-based phosphor activated with europium (III)

For the application of inorganic phosphors in solid-state lighting field, exploring a synthesis route with low energy consumption and low cost is the current research focus. In this study, a low-temperature solid-state synthesis route for a novel Li₂NaBP₂O₈:Eu³⁺ (LNBP:Eu) phosphor is reported. The phase structure, morphology, and elemental composition of its powder phase are characterized. According to photoluminescence and X-ray photoelectron spectroscopy data, the occupancy site and oxidation state of doping europium are discussed. Under near-UV (395 nm) excitation, the powder phase exhibits reddish-orange emission with a dominant ⁵D₀ → ⁷F₁ transition of europium. The intensity of visible photoluminescence is closely influenced by the europium doping content. The optimal content is 0.04 mol, and concentration quenching is ascribed to energy transfer among the nearest-neighbor europium ions. Moreover, chromatic properties are investigated in detail. The obtained data show that the LNBP:Eu powder phase is a prospective phosphor for application in near-UV-converted warm white light-emitting diodes.     

Green synthesis of aniline by phosphorus-doped titanium dioxide polymorphs

Phosphor doping in association with a heterostructure not only modifies the band structure of titanium dioxide (TiO₂) to make it more responsive to visible light, but it also suppresses its charge recombination and causes TiO₂ to have enhanced photoactivity. In this paper, we report on the controlled synthesis of phosphor-doped binary and ternary TiO₂ nanostructures through a hydrothermal method. The phase and morphology of the samples can be tuned by simply changing the hydrothermal time. Also, the visible-light photoactivity of the samples was evaluated by the reduction of nitrobenzene. The as-prepared catalysts exhibit enhanced photocatalytic activity in comparison to P₂₅ and the undoped counterpart, and the selected catalyst shows high photostability and photoactivity after reuse five times. These new TiO₂ nanostructures present a promising candidate for application in photocatalysis, photochemistry, sensors, and solar cells.     

Thermometry of red nanoflaked SrAl12O19:Mn4+ synthesized with boric acid flux

This paper presents the luminescence properties and potential of red SrAl₁₂O₁₉:Mn⁴⁺ (SAO:Mn⁴⁺) phosphor for optical thermometry application. The SAO crystal consisted of a spinel block along with two mirror-like blocks. The Al³⁺/Sr²⁺ molar ratio of the precursor solution affected the crystalline-phases, morphology, and photoluminescence of the phosphor. The addition of flux H₃BO₃ promoted the growth of hexagonal-nanoflakes and enhanced the external quantum efficiency of phosphor 2.6-fold. The absolute sensitivity S_a and relative sensitivity S_r of SAO:Mn⁴⁺ showed a linear function of the temperature. The value of S_a was 4.17?×?10^?3 K^?1, and the maximum S_r was 2.70?×?10^?3 K^?1 at 393?K. A stable emission color was observed even with a change in temperature and a bright red light was seen in both daylight and a darkroom.     

Direct correlation between reliability and pH changes of phosphors for white light-emitting diodes

The reactivity of phosphor with water was investigated by measuring pH change, and the results are compared with long-term reliability test results as well as scanning electron microscope (SEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) results. We found that the slope of pH change strongly depends on phosphor composition and represents a long-term reliability test result induced by phosphor in an LED package.     

Improved photoluminescence,thermal stability and temperature sensing performances of K+ incorporated perovskite BaTiO3:Eu3+ red emitting phosphors

K⁺ ions incorporated perovskite Ba_(1−x)TiO₃:x Eu³⁺ red emitting phosphors synthesized via facile solid -state reaction method has been investigated in the current study. The photoluminescence and decay time behavior of Ba_(1−x−y)TiO₃:x Eu³⁺,yK⁺ phosphors are investigated as a function of Eu³⁺, K⁺ concentration and temperature. An intense and sharp emission peak at 615 nm was exhibited by the phosphors upon excitation at 397 nm (⁷F₀→⁵L₆). It can be credited to the hypersensitive electric dipole transition ⁵D₀→⁷F₂, which confirms that Eu³⁺ ions are located at non-centrosymmetric site of the host. The incorporation of K⁺ ions in optimized Ba_0.95TiO₃:0.05 Eu³⁺ phosphor resulted in a remarkable enhancement of photoluminescence intensity by 2.33 times as compared to bare one. The Ba_0.89TiO₃:0.05 Eu³⁺, 0.06 K⁺ phosphors were found to observe good temperature sensing along with adequate thermal stability even at 427 K. Furthermore, the photometric parameters have been also studied which are strongly facilitate the prepared ceramic samples as suitable for potential application in lighting.     

Host sensitized near-infrared emission in Nd3+-Yb3+ Co-doped Na2GdMg2V3O12 phosphor

Yb³⁺/Nd³⁺ singly and co-doped Na₂GdMg₂V₃O₁₂ phosphors with near-infrared (NIR) emission were synthesized via sol-gel method. The phase purity and structure of samples were characterized by X-ray diffraction (XRD), the photoluminescence emission (PL) and excitation (PLE) spectra along with decay curves were also measured. Near infrared (NIR) emissions (850–1150 nm) from acceptors Yb³⁺ or Nd³⁺ matching well with the response curve of the silicon solar cell were obtained, in which VO₄³⁻ groups acted as sensitizers by capturing near ultraviolet photons which are not absorbed efficiently by silicon solar cell and transferred them to Yb³⁺/Nd³⁺ by energy transfer processes. The NIR emission intensities of the Nd³⁺-Yb³⁺co-doped samples Na₂GdMg₂V₃O₁₂ were enhanced greatly in comparison with that of Nd³⁺/Yb³⁺ singly doped samples, and the possible energy transfer processes were also discussed in detail. Results indicate that the obtained samples are potential solar spectral down-conversion (DC) convertors to enhance the conversion efficiency of the silicon solar cells.