A low cost and high efficient Ba9(Lu2-x-yAlx)Si6O24:yCe3+ cyan-emitting phosphor

White LEDs constructed by near-ultraviolet chips and red/green/blue/cyan-emitting phosphors are an important route for healthy lighting. However, efficient cyan-emitting phosphors are quite scarcity. The cyan-emitting phosphor Ba₉Lu_1.5Al_0.5Si₆O₂₄:Ce³⁺ (BLASO:Ce³⁺) was reported for the first time. Under 400 nm excitation, BLASO:Ce³⁺ shows a emission peak at 488 nm with an FWHM of about 117 nm. At room temperature, the internal quantum efficiency (IQE) can reach as high as 90.8%. At 150 °C, the IQE decreases to 81.5%, indicating an excellent thermal stability. The effect of the Al substitution for Lu on crystal structures and photoluminescence were investigated. The homogeneity of the luminescence was diagnosed by viewing microscopic particles based on the scanning electron microscope (SEM) equipped a cathodoluminescence (CL) system.     

Improved thermal stability and luminescence properties of SrSi2O2N2:Eu2+ green phosphor by a heterogeneous precipitation protocol for solid-state lighting applications

The SrSi₂O₂N₂:Eu²⁺ green-emitting phosphor, as a member of oxynitride phosphors, could greatly enhance the color quality of the white-light conversed by single yellow-emitting phosphor. However, SrSi₂O₂N₂:Eu²⁺ phosphors prepared by traditional solid-state ways normally consist hard agglomerates with unevenly dispersed particles and therefore suppress the luminescence properties. This research proposes a heterogeneous precipitation protocol where precipitation process is introduced, in order to produce a precursor in the first phase. And in the second phase, a high-temperature solid-state process is adopted for obtaining the final product. The main results show that, for an optimized SrSi₂O₂N₂:Eu²⁺ phosphor prepared using our protocol, (1) the SrSi₂O₂N₂:Eu²⁺ particles are faceted and with smooth faces and (2) the phosphor photoluminescence, external quantum efficiency, stability against thermal exposure, and physical stability consistently outperform the current commercially used product. This research essentially provides an economic way for production of solid-state lighting with enhanced color quality.     

Synthesis and photoluminescence of novel blue-emitting phosphor of Eu2+-activated fluoroborate BaGaBO3F2

Pure and Eu²⁺-activated fluoroborate BaGaBO₃F₂ was prepared using high-temperature solid-state reaction. BaGaBO₃F₂ is a wide band semiconductor with the indirect transition characteristic. The excitation and luminescence spectra of the phosphor were measured, and it was found that Eu²⁺-activated BaGaBO₃F₂ exhibits a bright blue color under ultraviolet (UV) light. The narrow emission band peaked at 425 nm is attributed to the transitions of 4f⁶5d→4f⁷(⁸S_7/2), and the Stokes shift estimated for this phosphor sample is 3140 cm⁻¹. The lifetime of the luminescence is also reported. The absolute quantum efficiency (QE) of the phosphor was evaluated, and it was found that the absolute QE decreases with increasing Eu²⁺ concentration. The phosphor shows an excellent quantum efficiency of 72.5% and a high thermal activation energy of 0.342 eV. The study concludes that Eu²⁺-doped BaGaBO₃F₂ phosphor has promising luminescence application abilities and can be used as a blue-emitting phosphor in a variety of applications.     

Efficient,stable, broadband cyan-emitting Ca-substituted Ba9Lu2Si6O24:Eu2+ with multisite luminescence for NUV-wLEDs

In order to develop an efficient and stable broadband cyan phosphor for full spectrum white lighting emitting diodes (wLEDs), novel Ba₉Lu₂Si₆O₂₄:Eu²⁺, xCa²⁺ is designed and synthesized. Ca-substitution induces Eu²⁺ ions into Lu³⁺ crystallographic site, which achieve rare nonequivalent cation substitution of Eu²⁺. Effects of Ca-substitution on crystal structure of matrix and phosphor are investigated by X-ray photoelectron spectroscopy, X-ray powder diffraction, transmission electron microscopy, and density functional thoery (DFT). Ba₉Lu₂Si₆O₂₄:Eu²⁺, xCa²⁺ can be effectively excited by with near-ultraviolet (NUV) and exhibit broadband cyan emission with full width at half maximum (FWHM) of 119.7 nm at x = 0.2, due to the multisite luminescence centers. For the sample x = 0.2, the internal quantum efficiency is 92.61%, and the luminous intensity at 423 K remains 89% of that measured at room temperature. The rigid structure of [SiO4]-[LuO6]-[SiO4] doped with Eu2+ ion makes Ca-substituted samples exhibit excellent luminescence efficiency and thermal stability. Our work develops a significant strategy based on multisite cation regulation to explore NUV-excited broadband cyan phosphors for full spectrum wLEDs.     

Phase formation and spectral evolution of (Sr,Ba)2Si(O,N)4:Eu2+ phosphors

Sr_2‐xBa_xSi(O,N)₄:Eu²⁺ (SB_xSON:Eu²⁺) oxynitridosilicate phosphors were prepared via incorporation of N^3?, Eu²⁺, and Ba²⁺ ions into Sr₂SiO₄ (SSO) lattices. X‐ray diffraction patterns of the prepared powders revealed that SB_xSON:Eu²⁺ was a solid‐solution form of SSO. An increase in x values caused a phase transition and an expansion of the unit cell. The photoluminescence excitation (PLE) spectra of SB_xSON:Eu²⁺ were broad, covering the ultraviolet range to the visible range. Corresponding PL emission spectra strongly depended on the excitation wavelengths and consisted of two emission bands, one in the green‐blue region (A‐band) and the other in the red region (B‐band), which were assigned to Eu(I) and Eu(II), respectively. The B‐band resulted from a dramatic red‐shift of the green emission band assigned to Eu(II) of SSO:Eu²⁺, revealing that the nitridation process preferentially affected the Eu(II) sites. This behavior was explained by crystal field splitting, the fluorescence decay time, and thermal quenching. The Ba²⁺ substitution caused evolution of the PL spectra, and its effects on the spectra were discussed under consideration of ionic size and covalence.     

Green emitting Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ phosphor with high thermal emission stability for warm WLEDs and FEDs

By hetero-valence substituting Ba²⁺-Si⁴⁺ for Lu³⁺-Al³⁺ pair in Lu₃Al₅O₁₂: Ce³⁺, a new green phosphor Ba_1.5Lu_1.5Al_3.5Si_1.5O₁₂: Ce³⁺ (BLAS: Ce³⁺) has been obtained. It crystallizes in garnet structure with space group Ia-3d (230). In the structure, Ba²⁺ ions are incorporated into both dodecahedral Lu³⁺ and octahedral Al³⁺ sites while Si⁴⁺ ions only occupy tetrahedral Al³⁺ sites. Under the blue light irradiation of 450 nm, an intense green light peaking at 520 nm was observed and the PL spectrum can be fitted in two Gaussian components, due to the crystal field splitting of Ce³⁺ 5d states under D₂ symmetry constrains. The optical doping concentration of BLAS: Ce³⁺ is 6% mol, of which the IQE and EQE are 89.1% and 51.8%, respectively. Furthermore, this sample exhibits an extremely good thermal stability, i.e. the integrated emission intensity is still more than 90% of the initial intensity at 480 K. Then, a w-LED device was fabricated from this new green phosphor BLAS: Ce³⁺ and commercial red phosphor (Ca,Sr)AlSiN₃: Eu²⁺, which shows a quite high color rendering (Ra = 88.2) and a relatively low color temperature 4772 K. Besides, the phosphor exhibits a stable chromaticity under different acceleration voltages. The phosphor may be promising material for the development of solid-state lighting and display systems.     

Structure analysis,tuning photoluminescence and enhancing thermal stability on Mn4+-doped La2-xYxMgTiO6 red phosphor for agricultural lighting

Currently, phosphor-converted LEDs (pc-LEDs) are revolutionizing the industry of plant growth lighting. To meet the requirements of this technology, phosphors with tunable photoluminescence, high thermal stability and luminous intensity are required. Herein, we found that the simple substitution of yttrium for lanthanum in La₂MgTiO₆:Mn⁴⁺ (LMT:Mn⁴⁺) system could satisfy above three criteria simultaneously. The photoluminescence properties can be regulated by continuously controlling the chemical composition of La_2-xY_xMgTiO₆:Mn⁴⁺ solid solution. The La sites are occupied by Y ions, causing a significant blue shift in the emission spectra which owing to the change of local crystal field strengthen. Meanwhile, the thermal stability and decay lifetimes are also varied due to the variation of local structure and band gap energy. The thermal stability of the material reaches 83.5% at 150 °C, which is better than the reported La₂MgTiO₆:Mn⁴⁺ and Y₂MgTiO₆:Mn⁴⁺ phosphors. The electronic luminescence (EL) of pc-LED devices using La_2-xY_xMgTiO₆:Mn⁴⁺ red phosphor is evaluated, which matching the absorption regions of plant pigments well, reflecting the superiority of the studied phosphors in plant growth lighting areas.     

Eu2+ activated NaBa3Si2O7F: A new efficient blue-emitting luminescent material for solid-state lighting and display

Exploring novel efficient phosphors for lighting and display has always been an important and meaningful work for researchers. Herein, a novel efficient blue-emitting phosphor, Eu²⁺ doped barium-containing silicate fluoride NaBa₃Si₂O₇F, was prepared by solid-state method. The phosphor can produce bright blue light peaked at 452 nm with full-width at half-maximum about 57 nm under near-UV light excitation, and it exhibits a high internal quantum yield about 76.23%. The temperature-dependent photoluminescence spectra show that this phosphor owns good thermal stability, and the emission intensity at 425 K is 67% of that at room temperature. The outstanding data of fabricated device demonstrate that the blue phosphor has large possibility of practical application for white light-emitting diode. Furthermore, the phosphor also possesses good cathodoluminescence properties under various accelerating voltage with different probe currents, indicating its potential application in field emission displays.     

Effects of the deep traps on the thermal‐stability property of CaAl2O4: Eu2+ phosphor

The thermal quenching properties and mechanisms of phosphors employed in white light emitting diodes (wLEDs) are critical for their commercial application. Here, we attempted to characterize the deep traps for capturing and releasing carriers to improve the thermal stability of the blue‐emitting CaAl₂O₄: Eu²⁺, Tm³⁺ phosphors. The enhanced thermal stability contributed to the introduction of traps has been demonstrated, and the mechanism of the transport process of carriers, has been explored in detail. In comparison with Eu²⁺ doped sample, the co‐doped Tm³⁺ samples bring more deep traps. The releasing of carriers in deep traps therefore sustains the luminescence with increasing temperature and compensates the thermal luminescence intensity loss. The results provide a theoretical basis and new field of view for exploring excellent thermal stability phosphors for wLEDs.     

High luminescent brightness and thermal stability of red emitting Li3Ba2Y3(WO4)8:Eu3+ phosphor

A series of Li₃Ba₂Y_3−x(WO₄)₈:xEu³⁺ (x=0.1, 1, 1.5, 2 and 2.8) phosphors were synthesized by a high temperature solid-state reaction method. Under the excitation of near ultraviolet (NUV) light, the as-prepared phosphor exhibits intense red luminescence originating from the characteristic transitions of Eu³⁺ ions, which is 1.8 times as strong as the commercial Y₂O₂S:Eu³⁺ phosphor. The optimal doping concentration of Eu³⁺ ions here is confirmed as x=1.5. The electric dipole-quadrupole (D-Q) interaction is deduced to be responsible for concentration quenching of Eu³⁺ ions in the Li₃Ba₂Y₃(WO₄)₈ phosphor. The analysis of optical transition and Huang-Rhys factor reveals a weak electron-phonon coupling interaction. The temperature-dependent emission spectra also indicate that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor has better thermal stability than that of the commercial Y₂O₂S:Eu³⁺ phosphor. Therefore, our results show that the as-prepared Li₃Ba₂Y₃(WO₄)₈:Eu³⁺ phosphor is a promising candidate as red emitting component for white light emitting diodes (LEDs).     

Design of a narrow-band blue-emitting Rb2Ba3(P2O7)2:Eu2+ phosphor with low thermal quenching for plant growth LEDs

Phosphor-converted light-emitting diodes (pc-LEDs) are commonly used to regulate the light environment to control the growth rates and improve the production efficiency of plant. Among them, the exploration of blue-emitting phosphors with high efficiency, low thermal quenching and excellent spectrum resemblance matching with the plant response spectrum is still challenging. Herein, a narrow-band blue-emitting Rb₂Ba₃(P₂O₇)₂:Eu²⁺ phosphor with high color purity of 93.4% has been developed. Under 345 nm excitation, it exhibits a blue emission band centered at 413 nm with a full width at half-maximum (FWHM) of 36 nm, and the emission spectrum of Rb₂Ba₃(P₂O₇)₂:0.060Eu²⁺ sample shows 85.7% spectrum resemblance with the absorption spectrum of chlorophyll-a in the blue region from 400 to 500 nm. In addition, the temperature-dependent emission spectra demonstrate that the Rb₂Ba₃(P₂O₇)₂:0.060Eu²⁺ phosphor has good thermal stability and small chromaticity shift, with the emission intensity dropping to 72.5% at 423 K of the initial intensity at 298 K and a chromaticity shift of 38 × 10^-3 at 498 K. All results suggest that the blue-emitting Rb₂Ba₃(P₂O₇)₂:Eu²⁺ phosphor has potential application in plant growth LEDs.     

A far-red-emitting (Gd,Y)3(Ga,Al)5O12:Mn2+ ceramic phosphor with enhanced thermal stability for plant cultivation

As for plants, far-red (FR) light with wavelength from 700 nm to 740 nm is critical for processes of photosynthesis and photomorphogenesis. Light-controlled development depends on light to control cell differentiation, structural and functional changes, and finally converge into the formation of tissues and organs. Phosphor converted FR emission under LED excitation is a cost-effective and high-efficient way to provide artificial FR light source. With the aim to develop an efficient FR phosphor that can promote the plant growth, a series of gadolinium yttrium gallium garnet (GYGAG) transparent ceramic phosphors co-doped with Mn²⁺ and Si⁴⁺ have been fabricated via chemical co-precipitation method, followed sintered in O₂ and hot isostatic pressing in this work. Under UV excitation, the phosphor exhibited two bright and broadband red emission spectra due to Mn²⁺: ⁴T₁ → ⁶A₁ spin-forbidden transition, and one of which located in the right FR region. And then, Ce³⁺ ions were co-doped as the activator to enhance the absorption at blue light region and the emission of Mn²⁺. It turns out that the emission band of GYGAG transparent ceramic phosphors matches well with the absorption band of phytochrome P_FR, which means they are promising to be applied in plant cultivation light-emitting diodes (LEDs) for modulating plant growth. Besides, the thermal stability of this material was investigated systematically, and an energy transferring model involves defects was also proposed to explain the phenomenon of abnormal temperature quenching.     

White‐emitting phosphor Ba2B2O5:Ce3+, Tb3+, Sm3+: Luminescence,energy transfer,and thermal stability

A series of Ba₂B₂O₅: RE (RE=Ce³⁺/Tb³⁺/Sm³⁺) phosphors were synthesized using high‐temperature solid‐state reaction. The X‐ray diffraction (XRD), luminescent properties, and decay lifetimes are utilized to characterize the properties of the phosphors. The obtained phosphors can emit blue, green, and orange‐red light when single‐doped Ce³⁺, Tb³⁺, and Sm³⁺. The energy can transfer from Ce³⁺ to Tb³⁺ and Tb³⁺ to Sm³⁺ in Ba₂B₂O₅, but not from Ce³⁺ to Sm³⁺ in Ce³⁺ and Sm³⁺ codoped in Ba₂B₂O₅. However, the energy can transfer from Ce³⁺ to Sm³⁺ through the bridge role of Tb³⁺. We obtain white emission based on energy transfer of Ce³⁺→Tb³⁺→Sm³⁺ ions. These results reveal that Ce³⁺/Tb³⁺/Sm³⁺ can interact with each other in Ba₂B₂O₅, and Ba₂B₂O₅ may be a potential candidate host for white‐light‐emitting phosphors.     

Tunable dual-mode emission with excellent thermal stability in Ca4ZrGe3O12:Eu phosphors prepared in air for NUV-LEDs

Novel dual valence Eu-doped Ca₄ZrGe₃O₁₂ (CZGO) phosphors were successfully fabricated in air atmosphere through a solid-state route. Their crystal structure, photoluminescence properties as well as thermal quenching performance were investigated systematically. The spectra show that part of Eu³⁺ were reduced to Eu²⁺ and the mechanism is interpreted by the charge compensation. By altering Eu concentration, multi-color luminescence covering from blue to red is realized when irradiated by 370 nm light, which perfectly matches with the near ultraviolet (NUV) light-emitting diode (LED) chips. More importantly, under NUV excitation, luminescent intensities are almost unchanged even up to 423 K. And chromaticity exhibits only a tiny shift with growing temperature. Such suitable luminescent spectra and superior thermal stability indicate that CZGO:Eu phosphors are promising candidates for blue-red components in NUV pumped W-LEDs. Finally, the fabricated W-LED based on the combination of CZGO:Eu phosphors, Ba₂SiO₄:Eu²⁺ and a 365 nm NUV-LED chip gives a high color rendering index, a low correlated color temperature and suitable CIE chromaticity coordinates.     

Highly efficient yellow-orange emission and superior thermal stability of Ba2YAl3Si2O12:Ce3+ for high-power solid lighting

With great economic benefits, white LEDs (w-LEDs) have aroused worldwide attention. For phosphor-converted w-LED, highly efficient emission and good thermal stability of phosphor are significant parameters in practical application. Here, a yellow-orange garnet-structural phosphor, Ba₂YAl₃Si₂O₁₂:xCe³⁺ (x = 0-0.1) (BYAS:xCe³⁺) was developed by solid solution design. The broad emission spectrum of the as-synthesized phosphor could guarantee the effective increase of the color rendering index when it is combined with the InGaN blue chip. Benefiting from the garnet-type highly rigid framework, BYAS:xCe³⁺ exhibits an excellent thermal stability (50%@673K of the initial integrated intensity at 280 K) as well as high absolute quantum efficiency (80.4%@460 nm excitation light). Utilizing the approach of “phosphor-in-glass” (PiG), a high-power warm w-LED is achieved based on a blue LED plus PiG and the illuminance of this w-LED device can be as high as 4227 lx.     

Effect of Ga3+ ion doping on emission thermal stability and efficiency of MgAl2O4:Cr3+ phosphor

In this work, we fabricated a novel spinel-type phosphor material MgAl_2−xGa_xO₄ doped with Cr³⁺ by the high-temperature solid-state sintering method. The crystal field environment of the spinel was tuned by replacing the Al ions with Ga³⁺ ions of different concentrations. The cell volume and D_q/B gradient increase from 2.82 to 2.62 with increasing Ga³⁺ ion doping concentration. This also implies a gradual decrease in the field strength of the crystal. Based on this, the excitation spectra of MgAl_1.995−xGa_xO₄:0.5%Cr³⁺ phosphors yield a redshift. Increasing the Ga³⁺ ion doping concentration also improves the emission intensity and thermal stability of the phosphors, and the emission intensity of the Ga³⁺-doped phosphors is significantly increased. For a Ga/Al ratio of 1, the thermal stability of the phosphor emission is optimal. The emission intensity at 140°C can maintain 76% of the emission intensity at room temperature, indicating that appropriate Ga³⁺ ion doping can improve the emission efficiency and thermal stability of the phosphors.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

Enhanced luminescence and thermal stability of (Sr,Ca)AlSiN3:Eu2+ via superficial organic carbon modification

The Eu²⁺-activated nitride phosphors have been widely used in solid-state lighting, but the applications in high-power white-light-emitting diodes (wLEDs) field require higher thermal stability of luminescent materials. The oxidation of Eu²⁺ and the damage of nitride host in the Eu²⁺-activated nitride phosphors are the two crucial reasons for the luminescence loss while operating. A superficial organic carbon modification is performed on the red-emitting (Sr,Ca)AlSiN₃:Eu²⁺ phosphor via the incorporation of organic carbon by solution mixing and thermal post-treatment under the N₂-H₂ atmosphere. After the superficial organic carbon modification, the oxidation of Eu²⁺ and the formation of impurity phases on the phosphor surface are effectively reduced. When the superficial organic carbon modified sample was treated in the 2 wt.% sucrose solutions, the relative brightness is strengthened by 2.15%, the thermal quenching characteristic is improved by 8.9% at 300℃, and the aging test results show an excellent thermal stability. All above indicate that the superficial organic carbon modification is a promising technique to enhance the thermal stability of analogous Eu²⁺-activated nirtide phosphors.     

Efficient near-infrared pyroxene phosphor LiInGe2O6:Cr3+ for NIR spectroscopy application

Broadband near-infrared phosphors are essential to realize nondestructive analysis in food industry and biomedical areas. Efficient long-wavelength (>830 nm) phosphors are strongly desired for practical applications. Herein, we demonstrate an efficient broadband NIR phosphor LiInGe₂O₆:Cr³⁺, which exhibits a broad NIR emission peaking at ~880 nm with a full width at half maximum of 172 nm upon 460 nm excitation. The internal/external quantum efficiencies of LiInGe₂O₆:Cr³⁺ are measured to be 81.2% and 39.8%, respectively. The absorption of the phosphor matches well with commercial blue LEDs. Using the fabricated phosphor converted LED illuminating human palm, distribution of blood vessels can be clearly recognized under a NIR camera. These results indicate that LiInGe₂O₆:Cr³⁺ is a promising candidate to be used in future non-destructive biological applications.     

Enhancing emission intensity and thermal stability by charge compensation in Sr2Mg3P4O15:Eu3+

Charge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr₂Mg₃P₄O₁₅:Eu³⁺ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R⁺ (R⁺ = Li, Na, and K), substituting Si⁴⁺ for P⁵⁺ and self‐compensation) were employed to solve the charge imbalance problem between Sr²⁺ and Eu³⁺. The results showed that emission intensity of Eu³⁺ was improved by 1.43 (Li⁺), 1.58 (Na⁺), 1.53 (K⁺), 1.61 (Si⁴⁺), and 1.30 (self) times than that of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr_1.6Mg₃P₄O₁₅:0.40Eu³⁺ to 55.69% (Li⁺), 61.62% (Na⁺), 58.98% (K⁺), 71.15% (Si⁴⁺), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor.