Narrow Results

New results on NIR emission in Li₃Ba₂La₃(WO${}_4{)}_8$:Nd${}^{3+}$ prepared by the SSR method are reported. Prepared sample is examined by XRD for crystal structure confirmation. This compound crystallizes into the monoclinic crystal system with space group C2/c (No.15) having lattice parameters $a=5.323\AA ,b=13.091\AA ,c=19.48$Å, $\beta =91.18^{\circ }$, and $Z=2$. The photoluminescence recorded with 588nm (⁴I${}_{9/2}{\to }^4$F${}_{5/2})$ excitation shows characteristic line emission in the NIR region, with the most intense emission at 1069nm (⁴F${}_{3/2}{\to }^4$I${}_{11/2}$). Concentration quenching was observed for Nd${}^{3+}$ contents exceeding 2 mol%. The calculated critical distance is 40.16 Å.

A series of singly and co-doped LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$, Tb${}^{3+}$ phosphors prepared by solid state metathesis (SSM) was reported the first time. The X-Ray diffraction (XRD) verified that the as-prepared materials exhibit a pure rhombohedral phase with a space group of P2₁/m. Scanning electron microscopy (SEM), Energy Dispersive X-ray analysis (EDAX) and elemental mapping confirm the morphology and constituents of elements. The LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$ shows 614nm red emission obtained due to the ⁵D${}_0{\to }^7$L₆ transition under 393nm excitation and the Tb${}^{3+}$ doped sample gives 546nm green emission ascribed to ⁵D${}_4{\to }^7$F₅ for excitation of 376nm. The luminescence properties of Eu${}^{3+}$/Tb${}^{3+}$ doped LiTi₂(PO${}_4{)}_3$ phosphors excited under a UV source were investigated and the relative mechanism was analyzed. Upon excitation by 393nm, the LiTi₂(PO${}_4{)}_3$:Eu_xTb_y phosphor has the capability to generate vivid green, yellow and red emissions, with color tunability achieved through the modulation of dopant ion concentrations. Color chromaticity of LiTi₂(PO${}_4{)}_3$:Eu${}_{0.01}$Tb${}_{0.05}$ gives at $x=0.574$, $y=0.425$ and $\mathrm{\text{CCT}}=1810.04$K. The proposed simple, low-cost, nontoxic and rapid synthesis route of phosphate-based compounds will lead the way to access these LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$/Tb${}^{3+}$ phosphors for potential applications in w-light-emitting diodes and plasma display panel.

Transparent mesoporous TiO₂ films consisting of uniform anatase particles have been deposited on glass slides by using sol-gel technique. A Europium complex Eu(TTA)₃(bpy), where the TTA ligand is β-diketonate thenoyltrifluoroacetonate and the bpy is 2,2-bipyridine, was formed on TiO₂ surface by physical adsorption of europium ions and successive formation of stable chelate complexes with TTA and bpy ligands. In this way a well dispersion of the complex has been achieved giving significant emission intensity. The excitation of the material in the UV region (374 nm) results in the emission of a nearly monochromatic light at 613 nm (⁵D₀→⁷F₂) via energy transfer from the excited organic ligands to europium emissive state.

Y₃Al₅O₁₂:Ce and (Y,Gd)₃Al₅O₁₂:Ce powder phosphors were prepared by a citric-gel method by using metals nitrates as starting materials and citric acid as a complexing agent. Single phase of Y₃Al₅O₁₂:Ce was obtained by firing a precursor of the metal-citrate complexes at as low as 1000°C for 5 hours. All the Y₃Al₅O₁₂:Ce phosphors showed broad emission peaks in the range of 480-650nm and had the maximum intensity at 529nm, which were stimulated by blue-LEDs. Excitation spectra of Y₃Al₅O₁₂:Ce with different concentrations of Ce showed that the optimum amount of the doping was 1mol% for best luminescence. The photoluminescent wavelength of the (Y,Gd)₃Al₅O₁₂:Ce (Ce:1mol%) increased monotonically with increasing the amount of Gd concentration (up to 560nm for Gd₃Al₅O₁₂:Ce), in accordance with a linear increase of their lattice constant (e.g. 12.01Å for Y₃Al₅O₁₂:Ce and 12.11Å for Gd₃Al₅O₁₂:Ce).

The paper deals with low-temperature photoluminescence and deformation luminescence (mechanoluminescence) of a composite material based on fine disperse powder of phosphor SrAl₂O₄:(Eu²⁺, Dy³⁺) and photopolymerizing resin that is transparent in the visible region. New information about the energy levels of impurities and defects was obtained. It has been found that at low temperatures (T = 15 ÷ 200 K) the photoluminescence spectrum of SrAl₂O₄:(Eu²⁺, Dy³⁺) presents two partially overlapping wide bands with the maxima at λ_1max = 446 nm and λ_2max = 517 nm. The strong interaction of energy states of the bands results in temperature quenching of the short-wave band of luminescence (λ_1max = 446 nm) and its complete attenuation at T ≥ 200 K. The results were used to describe the mechanism of persistent luminescence and mechanoluminescence of SrAl₂O₄:(Eu²⁺, Dy³⁺).

In this paper, NaYGeO₄:$x$Bi${}^{3+}$ phosphors were successfully prepared by high-temperature solid-state reaction. XRD patterns and refinement results show that Bi${}^{3+}$ ions are successfully incorporated into the matrix material and replaced by Y${}^{3+}$. The emission spectrum shows that the optimal doping concentration of the sample is 0.25%, and it is theoretically studied that the concentration quenching is caused by the nearest neighbor ions. The fluorescence lifetime curve showed that with the increase of Bi${}^{3+}$ concentration, the fluorescence lifetime first increased and then decreased. The thermal stability of the sample was studied, and it was found that when the temperature increased to 523 K, the luminescence intensity of the phosphor was still 70% of the initial intensity, and the activation energy was calculated to be 0.306 eV. Finally, the CIE color coordinates of the sample with the best luminous intensity were calculated as (0.1595, 0.0342), and the color coordinates are located in the blue light region.

Using Eu₂O₃, BaCO₃, Si₃N₄ and SiO₂ as starting materials, we succeeded in synthesizing BaSi₄O₆N₂:Eu${}^{2+}$ by firing the mixture at 1100^∘C for 2h in a reducing atmosphere (N₂(95%)–H₂(5%)). As a result, a single phase was obtained by setting the charge composition ratio to Si/$\mathrm{\text{Ba}}=6$. When the Eu${}^{2+}$ activation amount was 1%, it showed a broad emission in the range of 400–600nm under the excitation light of ultraviolet rays at 320nm. This phosphor exhibited chromaticity coordinates of $(x,y)=(0.258,0.297)$ under irradiation with ultraviolet rays at 320nm and is thought to be a promising phosphor for ultraviolet-excited white LEDs.

NaCaYF₆ is the formula for gagarinite. Noting the lack of luminescence studies in this material, we synthesized it using the hydrothermal method and investigated the luminescence of several lanthanides. Characteristic luminescence of Eu${}^{3+}$, Dy${}^{3+}$, Sm${}^{3+}$ and Tb${}^{3+}$ was observed. Detailed results on photoluminescence emission and excitation spectra, lifetime, chromaticity coordinates and concentration dependence of emission intensity are presented. Except for Tb${}^{3+}$, which exhibits f-d excitation, the luminescence of other activators got quenched at 1mol % concentration. Eu${}^{3+}$ emission in this host was peculiar, in that the emissions from higher ⁵D states were observed. Luminescence characteristics are explained using the known energy level diagrams for the lanthanide activators.

The investigation of photoluminescence (PL) properties of Ca(Al${}_x$Ga${}_{1-x}{)}_2$S₄:Eu${}^{2+}$ solid solutions with $x$ = 0, 0.1, 0.2 and 0.3 synthesized for the first time was performed in wide temperature and excitation power density ranges. It is shown that PL intensity decreases by only 20–30% for different $x$ in the temperature range from 10 K to 300 K. The extreme stability of shape and position of the emission spectra was found in the range of excitation power density from $3.5\cdot 10^2$ W/cm² to $1.4\cdot 10^6$ W/cm² by nanosecond pulsed radiation. The reversible PL efficiency droop was only above 10⁴ W/cm² of excitation power density. The PL decay time constant was found to be of about 560 ns to 595 ns for $x$ ranging between 0.1 and 0.3 at room temperature.

The non-rare-earth phosphor Ca₂ZnMoO₆ has a luminescence of 375–655 nm and emits near-white light. This study investigated it as a down-shifting layer to improve the efficiency of commercial flexible solar cells. The first structure was a solar cell/thick-film Ca₂ZnMoO₆ phosphor layer (TLDU device); a controlled light source was shone on the top, and UV light was shone on the bottom. The second structure was a solar cell/thick-film Ca₂ZnMoO₆ phosphor layer with an Al reflective layer (TLDR device), and only a controlled light source was used. We compared the power output efficiencies of the two structures with the efficiency of a control device. When the $I$–$V$ properties of the three different devices were measured, the $V_{\mathrm{\text{oc}}}$ value underwent no apparent change, but the $I_{\mathrm{\text{sc}}}$ increased in the TLDU and TLDR devices. These results suggest that if placed on the bottom surface of commercial solar cells, Ca₂ZnMoO₆ phosphor could improve their efficiency.

Photoluminescence (PL) spectra, light flux, color temperatures and color coordinates of white light emitting diodes that are based on CaGa₂S₄:Eu${}^{2+}$–CaS:Eu${}^{2+}$ composite solution and industrial phosphor were analyzed. The study was carried out continuously for a 1000 h with two white LEDs which based on an exciting InGaN wavelength of 450 nm with a power of 10 W. Luminous flux and color temperatures were investigated during 200, 400, 600, 800 and 1000 h. All experiments were carried out for both CaGa₂S₄:Eu${}^{2+}$–CaS:Eu${}^{2+}$ and industrial phosphor and comparatively analyzed. Consequently, the application perspectives of CaGa₂S₄:Eu${}^{2+}$–CaS:Eu${}^{2+}$ composite solution in the white LEDs technologies are presented.

A molten salt-assisted method for the synthesis of Eu${}^{3+}$-doped bismuth molybdate (BMO: Eu${}^{3+}$) phosphor was proposed. (BMO: Eu${}^{3+}$) phosphors with different phase structures were obtained by changing the calcination temperature. The applications in LED devices and latent fingerprint recognition of the obtained product were explored. The results of structural characterizations and scanning electron microscope (SEM) photographs analysis prove that the products exhibit different crystal structures and morphologies with the change of calcination temperature. Based on the above findings, the as-prepared products have potential applications in the field of WLED and potential fingerprint recognition.

Y₂SiO₅:Ce³⁺ particles was synthesized by sol–gel process. In all samples treated at 1100°C, monoclinic X₁ phase for all cerium concentration. Luminescence spectra shows broad Ce³⁺ luminescence in Y₂SiO₅ host, which picks around 450 nm. The synthesized and calcined powders were characterized by thermogravimetry-differential scanning calorimeter (TG-DSC), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and photoluminescence spectra (PL).

This paper reports an approach for enhancing the luminescent properties of Y₂O₃:Eu³⁺ nanophosphors with cellulose, using a liquid phase precursor (LPP) process. The nanosized particles showed a powder X-ray diffraction pattern, corresponding to the reference, and were highly crystalline. The grain sizes of the samples synthesized at 600°C for 1 h were estimated to be approximately 19 nm. The particle sizes of the samples increased with increasing synthesis temperature and the morphology was cleaned and without impurities. In addition, all the samples had a smaller particle size than that of the commercial product. The PL spectrum consisted of weak bands at 581, 587, 593, and 599 nm, corresponding to the ⁵D₀ → ⁷F₁ transition, and sharp peaks with a maximum intensity occurring at approximately 610 nm, due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. These results suggest that Y₂O₃:Eu³⁺ is a promising alternative red-emitting phosphor for high efficiency resolution display applications.

Red-light-emitting phosphors based on Sr${}_{1.5}$Ca${}_{0.5}$SiO₄ activated by trivalent europium ions (Eu${}^{3+})$ were successfully synthesized using a solid-state reaction method, and their luminescence properties were investigated. The photoluminescence spectra of Sr${}_{1.5}$Ca${}_{0.5}$SiO₄:$x$ Eu${}^{3+}$ phosphors synthesized at different temperatures and times and with different Eu${}^{3+}$ concentrations revealed emission peaks at 591nm, 612nm and 655nm, which can probably be attributed to the transition of Eu${}^{3+}$ ions from ⁵D₀ to ⁷F_J (J = 1, 2 and 3). The emission intensities of the transitions from ⁵D₀ to ⁷F_J (J = 1, 2 and 3) increased as the synthesizing temperature rose for 2h. Comparison with the relevant International Commission on Illumination diagram showed that Sr${}_{1.5}$Ca${}_{0.5}$SiO₄:$x$ Eu${}^{3+}$ phosphors synthesized at different temperatures and times and with different Eu${}^{3+}$ concentrations all emitted red light, with phosphors synthesized at 1300^∘C and with concentrations of 1.5at.% yielding the maximum emission intensity. These results show Sr${}_{1.5}$Ca${}_{0.5}$SiO₄:1.5% Eu${}^{3+}$ to be a noteworthy red-light-emitting phosphor candidate for white light-emitting diodes (WLEDs).

A blue-emitting borophosphate KSrBP₂O₈: Eu²⁺ is synthesized and evaluated as a candidate for near ultraviolet white light emitting diodes. This phosphor shows strong excitation band in 250~420 nm, and a broad and asymmetry emission band with a tail on the long-wavelength side. According to investigating on the crystal structure, the asymmetry emission band results from the certain degree of substitutional disorder of Eu²⁺ in KSrBP₂O₈: Eu²⁺. The emission intensity of the optimal sample with 5% Eu²⁺ is reached to 89% of that of the commercial BaMgAl₁₀O₁₇: Eu²⁺ under excitation at 365 nm, and the quantum efficiency of the optimal sample is 48.9%. The results reveal that the potential application of KSrBP₂O₈: 5% Eu²⁺ as a blue-emitting UV convertible phosphor for white light emitting diodes is feasible.

The afterglow time of typical red-emitting phosphors is much shorter than those of green- or blue-emitting phosphors which afterglow time were longer than 1000 min. CaS has been used as an effective host material for afterglow phosphors because trapping centers can be easily created in the host by doping with an activator. This study reports on the effect of a reducing atmosphere on the afterglow properties of a red-emitting CaS:Eu²⁺,Pr³⁺ phosphor. The phosphor was prepared by reduction under an Ar-H₂ (5%) or H₂S atmosphere from a CaSO₄:Eu³⁺,Pr³⁺ phosphor prepared using a liquid phase method. Heating the CaSO₄:Eu³⁺,Pr³⁺ phosphor for 2 h under an Ar-H₂ (5%) atmosphere at 1050°C gave CaO as by-product in addition to CaS. The resulting phosphor exhibited red-emission at 646 nm originating from Eu²⁺ ions upon visible light irradiation, and gave some afterglow after cessation of visible light irradiation. Addition of Li⁺ ions extended the afterglow time of the phosphor as a result of a slight change in the CaS host structure. For preparation of a CaSO₄:Eu³⁺,Pr³⁺ phosphor under a H₂S atmosphere, a CaS monophase was obtained. The emission and afterglow of the phosphor were similar to that prepared under the Ar-H₂ (5%) atmosphere, but the afterglow time resulting from the CaS monophase was longer. The longest afterglow time obtained was about 60 min for a phosphor prepared under a H₂S atmosphere with an initial Li/Ca atomic ratio of 0.04.

A new red phosphor of strontium aluminate activated by Mn⁴⁺ was developed for high color rendering and warm white light-emitting diodes. The phosphor composition and conditions for synthesis were optimized through solid-state reaction. Meanwhile, the structure and morphology were investigated with XRD and SEM analysis. The results show that the 3SrO•5Al₂O₃ activated by 0.0005 M Mn fired at 1300°C in air ambient by adopting 2.5 wt.% AlF₃ as flux exhibits most efficient luminescence. A white LED device prototype with CIE (0.3291, 0.3571), CCT 5639 K, CRI Ra 92.6, and efficacy 63 lm/W driven at 20 mA has been packaged by pre-coating the red phosphor combined with a yellow one Y₃Al₅O₁₂:Ce³⁺ on a blue InGaN chip. The analysis of critical distance and luminescence quench reveal that the mechanism of energy transfer for luminescence is through dipole–dipole interaction.

The aim of the present investigation was to develop a phosphor to solve the flickering luminescence of alternating current (AC) light-emitting diodes (LED) by compensating the dark duration with appropriately persistent luminescence. The phosphor SrAl₂O₄:Eu²⁺ co-doped with Y³⁺ or Dy³⁺ was synthesized via solid-state reaction with H₃BO₃ as flux. The crystal structure and morphology were characterized by using X-ray diffraction (XRD) and Scanning Electron Microscope (SEM), respectively. The photoluminescence spectra were collected with a fluorescence spectrometer. The results demonstrated that appropriate amount of Y³⁺ or DY³⁺ doped was beneficial to suppress the by-product of Sr₄Al₁₄O₂₅ which easily co-existed with the SrAl₂O₄ phase brought by the flux of H₃BO₃. However, too much Y³⁺ or DY³⁺ doped resulted in the formation of another impurity phase, i.e., the yttrium aluminum garnet of Y₃Al₅O₁₂ and Dy₃Al₅O₁₂. Comparatively, the doped DY³⁺ was more helpful in prolonging the persistent luminescence, while Y³⁺ was more efficient in enhancing luminescence intensity. To demonstrate the feasibility of the phosphor applied in AC LEDs, a nearly white AC LED was fabricated by coating the phosphor on a blue AC LED chip. The persistent luminescence was radiated from the AC LED device after turning power off. Moreover, the effect of the phosphor on compensating the AC LED dark duration through persistent luminescence was revealed by using the Keyence VW-9000 High-speed Microscope for the first time.

A novel orange-red phosphor Ca₃B₂O₆:Sm³⁺, A⁺(A = Li, Na, K) has been synthesized by solid-state reaction at 950°C. The phase purity and photoluminescence (PL) behavior of the phosphor are studied in detail using the powder X-ray diffraction (XRD) technique and PL measurements. Ca₃B₂O₆:Sm³⁺ phosphor can be efficiently excited by near ultraviolet (n-UV) and blue light, and the emission spectrum consists of four emission peaks at 563, 599, 646 and 709 nm, generating bright orange-red light. When a cation A⁺ is introduced into Ca₃B₂O₆:Sm³⁺ as charge compensator, the emission intensity of Ca₃B₂O₆:Sm³⁺ is evidently enhanced, but the PL spectral profile is unchanged. The integral intensity of the emission spectrum of Ca_2.96Sm_0.02Na_0.02B₂O₆ excited at 401 nm is about 1.2 times than that of Y₂O₂S:Eu³⁺ commercial red phosphor. The CIE chromaticity coordinates of Ca_2.96Sm_0.02Na_0.02B₂O₆ phosphor were (0.608, 0.365), which are close to that of the commercial red phosphors Y₂O₃:Eu³⁺ (0.655, 0.345), Y₂O₂S:Eu³⁺ (0.622, 0.351) and Sr₂Si₅N₈:Eu²⁺ (0.620, 0.370).