Efficient Near‐Infrared Emission of Ce3+–Nd3+ CoDoped (Sr0.6Ca0.4)3(Al0.6Si0.4)O4.4F0.6 Phosphors for c‐Si Solar Cell

Ce³⁺, Nd³⁺ codoped (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6 phosphors were synthesized through the high‐temperature solid‐state reaction method. Luminescence spectra, absorption spectra, and decay lifetimes of these samples have been measured to prove the energy‐transfer process from Ce³⁺ to Nd³⁺. Under UV and blue light excitation, (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6:Ce³⁺,Nd³⁺ phosphors exhibit near‐infrared (NIR) emission, mainly peaking at 1093 nm and secondarily at 916 nm. The NIR emission matches well with the band gap of c‐Si. Results of this work suggest that the (Sr_0.6Ca_0.4)₃(Al_0.6Si_0.4)O_4.4F_0.6:Ce³⁺, Nd³⁺ phosphors have potential application as down‐shifting luminescent convertor for enhancing the photoelectric conversion efficiency of c‐Si solar cell.     

Decay Behavior in Ce3+‐doped La3Si6N11 and Lu3Al5O12 Phosphors

Ce³⁺‐activated light emitting diode (LED) phosphors have been extensively examined for photoluminescence, and have been the focus of many detailed structural studies. However, reports of the decay curves of Ce³⁺‐activated LED phosphors are rare. Although we have reported the decay behaviors of several Eu²⁺‐activated LED phosphors such as Sr₂SiO₄, Sr₂Si₅N₈, and CaAlSiN₃, we have never conducted an in‐depth study into the decay behavior for Ce³⁺‐activated LED phosphors. For this study, we investigated the decay curves of well‐known Ce³⁺‐activated LED phosphors such as La₃Si₆N₁₁ and Lu₃Al₅O₁₂. Similar to Eu²⁺‐activated LED phosphors, the decay behavior of Ce³⁺‐activated LED phosphors was sensitive to the Ce³⁺ concentration and to the detection wavelength. There was active nonradiative energy transfer between the Ce³⁺ activators located at different sites.     

Luminescence Properties and Energy Transfer of Ce3+,Tb3+‐Coactivatedβ‐SiAlON Phosphors

Using the solid‐state reaction method, Ce³⁺,Tb³⁺‐coactivated Si₅AlON₇ (Si_6?zAl_zO_zN_8?z, z = 1) phosphors were successfully synthesized. The obtained phosphors exhibit high absorption and strong excitation bands in the wavelength range of 240–440 nm, matching well with the light emitting‐diode (LED) chip. The ET from Ce³⁺ to Tb³⁺ ions in Si₅AlON₇:Ce³⁺,Tb³⁺ has been studied and demonstrated by the luminescence spectra and decay curves. Moreover, the phosphors show tunable emissions from blue to green by tuning the relative ratio of the Ce³⁺ to Tb³⁺ ions. Thermal quenching properties of Si₅AlON₇:Ce³⁺,Tb³⁺ had also been investigated and the quenching temperature is ~190°C. These results show that Si₅AlON₇:Ce³⁺,Tb³⁺ could be a promising candidate for a single‐phased color‐tunable phosphor applied in UV‐chip pumped LEDs.     

Li2SrSiO4:Ce3+, Pr3+ Phosphor with Blue,Red, and Near‐Infrared Emissions Used for Plant Growth LED

Ce³⁺/Pr³⁺ codoped Li₂SrSiO₄ (LSS) phosphors with blue, red, and near‐infrared (NIR) tri‐emission have been prepared via a high‐temperature solid‐state reaction method. Under the excitation of 200 to 400 nm near‐ultraviolet (n‐UV), the photoluminescence (PL) spectra of phosphors are composed of visible and NIR two parts. The former exhibits blue and red emission bands centered at around 428 nm from 5d–4f transition of Ce³⁺ and 611 nm from ¹D₂ → ³H₄ transition of Pr³⁺, those overlap with photosynthesis action spectra of plants and absorption spectra of chlorophylls and carotenoids. While the later presents a broad NIR emission band peaking near 1039 nm caused by the ¹G₄ → ³H₄ of Pr³⁺, matching with the absorption of bacteriochlorophyll. Their emission intensity ratios (B: R: NIR) could be tuned by altering the relative ratios of Ce³⁺ and Pr³⁺ concentration in the phosphors to meet the requirements of multifarious plants and bacteria. The efficient energy transfer from Ce³⁺ to Pr³⁺ takes place in the LSS host, which ascribed to an exchange interaction according to PL spectra and decay curves of phosphors. Results suggest that the present LSS: Ce³⁺, Pr³⁺ phosphors have great potential applications in plant growth n‐UV LED.     

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

A modified chemical vapor deposition (CVD) technique is used to synthesize the color‐tunable siliconitride Sr_2‐1.5x‐yCe_xEu_ySi₅N₈ (x = 0.000‐0.016 and y = 0.000‐0.020) phosphors. In comparison with the conventional solid‐state method, the CVD approach successfully improved the crystallinity, particle size distribution, and photoluminescence through the enhanced gas‐solid reaction. Under blue excitation, Sr_1.98Eu_0.02Si₅N₈ exhibited a red emission band at 618 nm. The incorporation of Ce³⁺ ions increased the emission intensity of Eu²⁺ ions by approximately 10% owing to the enhanced absorption and dipole‐dipole energy transfer process from Ce³⁺ to Eu²⁺ ions. It resulted in a shift of the emission colors from yellow to red region. The external and internal quantum efficiencies of Sr_1.906Ce_0.06Eu_0.004Si₅N₈ were calculated as 54% and 70%, respectively. The activation energy of thermal stability for Sr_1.906Ce_0.06Eu_0.004Si₅N₈ was evaluated as 0.31 eV. A white LED with a color rendering index of 80 and a CCT of 4964 K was successfully fabricated with the present phosphors. The current research demonstrated a new series of Sr₂Si₅N₈:Ce³⁺, Eu²⁺ phosphors with color‐tunability for fabricating white LEDs with high color‐rendering index.     

Improvement of photoluminescence properties of Ce3+- doped CaSrAl2SiO7 phosphors by charge compensation with Li+ and Na+

In this work, we prepared CaSr_1-xAl₂SiO₇:xCe³⁺ (0.03 ≤ x ≤ 0.12) and CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03 M⁺ (M⁺ = Li⁺ and Na⁺) phosphors via solid-state reaction method. Structural and photoluminescence (PL) properties of the phosphors were also investigated. The prepared phosphors formed an orthorhombic crystal structure with the P2₁2₁2₁ space group. CaSr_1-xAl₂SiO₇:xCe³⁺ phosphors were effectively excited by near-ultraviolet (UV) light (345 nm), which is suitable with the emission of near-UV light emitting diode chips. A broad blue emission (402 nm) was detected in CaSr_1-xAl₂SiO₇:xCe³⁺ and CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03 M⁺ phosphors; this was attributed to the 4f⁰5d¹ → 4f¹ transition of Ce³⁺. To maintain charge equilibrium, charge compensators, such as monovalent Li⁺ and Na⁺ ions, were doped into the CaSr_0.97Al₂SiO₇:0.03Ce³⁺ phosphor, significantly improving its PL properties. The strongest emission intensity was achieved in CaSr_0.94Al₂SiO₇:0.03Ce³⁺,0.03Li⁺ phosphor. Addition of Li⁺ charge compensator was highly effective in improving PL properties of CaSr_0.97Al₂SiO₇:0.03Ce³⁺ phosphors.     

Crystal Structure and Optical Performance of Al3+ and Ce3+ Codoped Ca3Sc2Si3O12 Green Phosphors for White LEDs

Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce) green phosphors used for white light‐emitting diodes (LEDs) are synthesized and codoped with Al³⁺ via a solid‐state reaction method. The crystal structure and vibrational modes are analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman scattering spectroscopy. The energy transfer behavior and optical performance are characterized by photoluminescence and excitation spectra, quantum efficiency, and time‐resolved photoluminescence. The incorporation of Al³⁺ into CSS:Ce can inhibit the formation of the impurity phases Sc₂O₃ and CeO₂, improve crystallinity, and enhance the photoluminescence intensity as well as quantum efficiency. The substitution of Sc³⁺ with Al³⁺ increased the crystal field splitting of Ce³⁺ and resulted in the red shift of photoluminescence. The results show that Ca₃Sc_2?xAl_xSi₃O₁₂:Ce³⁺ has high quantum efficiency, making it a promising green phosphor that can be collocated with a commercial 450 nm blue LED and a red phosphor for solid‐state lighting applications.     

Light‐induced electrons suppressed by Eu3+ ions doped in Ca11.94−xSrxAl14O33 caged phosphors for LED and FEDs

Control of light‐induced electron generation is of vital importance for the application of caged phosphors. For Eu‐doped Ca_11.94?xSr_xAl₁₄O₃₃ caged phosphors, the suppressed effect of strontium doping on the light‐induced electrons is observed compared to the europium‐free Ca_11.94?xSr_xAl₁₄O₃₃ phosphors. In the presence of europium ions, Sr doping will promote the reduction of Eu³⁺ to Eu²⁺. The Rietveld refinement suggests that unit cell volumes of the Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 samples are expanded when Ca²⁺ ions are replaced by Sr²⁺ ions. The absorption and FTIR transmittance spectra confirm that the competitive reaction of encaged O^2? anions with H₂ is suppressed. For the sample (x=0.48), the higher thermal activation energy (~0.40 eV) for luminescence quenching can be attributed to the more rigid framework structure after Sr doping. For Ca_11.94?xSr_xAl₁₄O₃₃:Eu_0.06 phosphors, their emission colours are tuned from red to purple upon 254 nm excitation and from pink to blue under electron beam excitation through Sr substitution. The insight gained from this work may have a significant guiding to design new phosphors for LED and FEDs and novel nanocaged mutifunctional materials.     

YBO3: Ce3+, Yb3+ based near-infrared quantum cutting phosphors: Synthesis and application to solar cells

Ce³⁺ and Yb³⁺ co-doped YBO₃ phosphors were facilely fabricated by a hydrothermal method. The investigations reveal that hexagonal YBO₃: Ce³⁺, Yb³⁺ nanoparticles aggregate to form cyclic structure after annealing at 900 °C. An efficient near-infrared (NIR) quantum cutting phenomenon involving the emission of two NIR photons (971 nm) for each ultraviolet (UV) photon (360 nm) absorbed is observed based on the cooperative energy transfer (CET) from Ce³⁺ to Yb³⁺ in YBO₃ with a CET efficiency of 41.9%. Moreover, YBO₃: Ce³⁺, Yb³⁺/SiO₂ films with anti-reflection and NIR quantum cutting abilities were prepared by dip-coating method. The as prepared composite films can convert UV photons into NIR photons between 950 nm and 1050 nm, which well matched with the spectral response of the silicon-based solar cell. The experimental results indicate that the photoelectric conversion efficiency of silicon solar cell can be effectively improved by assembling the YBO₃: Ce³⁺, Yb³⁺/SiO₂ bi-functional film, and the corresponding conversion efficiency is about 0.521% higher than the pure glass and 0.252% higher than the pure SiO₂ anti-reflection (AR) film. In a word, this work provides a simple strategy to develop optical films with AR and NIR quantum cutting abilities for solar energy conversion.     

Realizing broadband spectral conversion in novel Ce3+,Cr3+,Ln3+ (Ln = Yb,Nd, Er) tridoped near-infrared phosphors via multiple energy transfers

The solar spectral converters mainly involve the energy transfer between two codoped ions. Here, we report a series of Ce³⁺, Cr³⁺, Ln³⁺ (Ln = Yb, Nd, Er) tridoped Gd₃Sc₂Ga₃O₁₂ (GSGO) phosphors with improved absorption and increasing near infrared (NIR) emission. We observed the multiple energy transfer behaviors of Cr³⁺→Ln³⁺, Ce³⁺→Ln³⁺, Ce³⁺→Cr³⁺, and Ce³⁺→Cr³⁺→Ln³⁺ in GSGO matrix. When Ce³⁺ is introduced into the GSGO:Cr³⁺,Ln³⁺ phosphors, the energy transfer of Ce³⁺→Cr³⁺→Ln³⁺ has been realized by utilizing the energy transfer bridge of the Cr³⁺ ion. Consequently, GSGO:Ce³⁺,Cr³⁺,Ln³⁺ can absorb almost all ultraviolet and visible (UV–Vis) light and produce strong NIR light thanks to the synergistic effect of Ce³⁺→Cr³⁺→Ln³⁺, improving the photovoltaic conversion efficiency of c-Si solar cells. Our results show that the prepared GSGO:Ce³⁺,Cr³⁺,Ln³⁺ have the potential application in the solar spectral material for c-Si solar cells. Meanwhile, the strategy of multiple energy transfers gives a new way to design the spectral conversion materials with wider absorption for c-Si solar cells.     

Luminescence properties and energy transfer investigations of Sr2B2O5:Ce3+,Tb3+ phosphors

Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were synthesized by the solid-state method. X-ray diffraction (XRD) was used to characterize the phase structure. The luminescent properties of Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were investigated by using the photoluminescence emission, excitation spectra and reflectance spectra, respectively. The excitation spectra indicate that this phosphor can be effectively excited by near ultraviolet (n-UV) light of 317 nm. Under the excitation of 317 nm, Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors exhibited blue emission corresponding to the f–d transition of Ce³⁺ ions and green emission bands corresponding to the f–f transition of Tb³⁺ ions, respectively. The Reflectance spectra of the Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors are noted that combine with Ce³⁺ and Tb³⁺ ion absorptions. Effective energy transfer occurred from Ce³⁺ to Tb³⁺ in Sr₂B₂O₅ host due to the observed spectra overlap between the emission spectrum of Ce³⁺ ion and the excitation spectrum of Tb³⁺ ion. The energy transfer efficiency from Ce³⁺ ion to Tb³⁺ ion was also calculated to be 90%. The phosphor Sr₂B₂O₅:Ce³⁺,Tb³⁺ could be considered as one of double emission phosphor for n-UV excited white light emitting diodes.     

Broadband emission of single-phase Ca3Sc2Si3O12:Cr3+/Ln3+ (Ln = Nd,Yb, Ce) phosphors for novel solid-state light sources with visible to near-infrared light output

Novel single-component phosphors Ca₃Sc₂Si₃O₁₂:Cr³⁺/Ln³⁺ (CSS:Cr³⁺/Ln³⁺, Ln = Nd, Yb, Ce) with broadband near-infrared (NIR) emissions are synthesized. Their phase structure, photoluminescence properties and energy transfer between Cr³⁺ and Ln³⁺ ions are investigated. In the CSS host, Cr³⁺ ions occupy Sc³⁺ sites with low-field octahedral coordination, and thus show a broadband emission in 700–900 nm under the blue light excitation. Nd³⁺, Yb³⁺ and Ce³⁺ ions substitute Ca²⁺ sites in CSS, where Nd³⁺ and Yb³⁺ ions emit the NIR light in 900–1100 nm and their excitation efficiencies at ∼450 nm are greatly enhanced by utilizing the energy transfer from Cr³⁺ to Nd³⁺/Yb³⁺ ions. Ce³⁺ ions can further enhance the absorption of CSS:Cr³⁺/Ln³⁺ phosphors to the blue light, and at the same time contribute to the visible emission in 480–650 nm. Furthermore, CSS:Cr³⁺/Ln³⁺ phosphors show good thermal stability, and approximately 79% of the initial emission intensity is sustained at 150 °C. A phosphor-converted LED (pc-LED) prototype is fabricated by integrating the as-prepared phosphor CSS:Cr³⁺/Ln³⁺ and the commercial phosphor CaAlSiN₃:Eu²⁺ with the blue LED chip, showing a super broadband emission ranging from 450 to 1100 nm. This finding shows the potential application of CSS:Cr³⁺/Ln³⁺ phosphors in broadband NIR pc-LEDs or super broadband LED sources with visible to NIR light output.     

Dy3+/Ce3+ Codoped YAG Transparent Ceramics for Single‐Composition Tunable White‐Light Phosphor

Superior optical, thermal, and mechanical properties of transparent ceramics are very important in the applications of solid lasers, solid‐state lighting, and transparent armors. Herein, a series of (Dy_0.03Ce_xY_0.97?x)₃Al₅O₁₂ transparent ceramics were fabricated using vacuum reactive sintering method. Importantly, these Dy³⁺/Ce³⁺ codoped yttrium aluminum garnet (YAG) transparent ceramics served as single‐composition tunable white‐light phosphors for UV‐LEDs is developed for the first time. By combining with commercially available UV‐LEDs directly, the optimal chromaticity coordinates and correlated color temperature (CCT) are (x = 0.33, y = 0.35) and 5609 K, respectively. Notably, the codoping of Ce³⁺ enhances the luminescent intensity of Dy³⁺ ions while excited at 327 nm. The emission color of YAG transparent ceramics can be tuned from white to yellow through energy transfer between Dy³⁺ and Ce³⁺. These new phosphors, possessing of pure CIE chromaticity and environmentally friendly nature, are promising for applications in white UV‐LEDs.     

Eu‐Doped β‐SiAlON Phosphors: Template‐Assistant Low Temperature Synthesis,Dual Band Emission,and High‐Thermal Stability

A hard template route has been successfully developed for synthesis of β‐SiAlON:Eu phosphors at low temperatures. The synthesis utilizes mesoporous silica (SBA‐15) skeleton as an active Si source, combined with the carbothermal reduction and nitridation method. It has been shown that the additional driving force from high surface area and porosity of SBA‐15 enables β‐SiAlON:Eu (with compositions of Si_6?zAl_z?xO_z+xN_8?z?x: xEu, x = 0.010–0.200 and z = 1.000) phosphors to be formed as a dominant phase at low temperature of 1400°C. The resultant β‐SiAlON:Eu phosphor powders exhibit a typical rod‐like morphology and a well dispersed state. By tailoring the Eu²⁺ concentration in the phosphors, a continuous change in emission band can be realized, that is a blue emission dominated for low Eu²⁺ concentrations and a green emission dominated for high Eu²⁺ doping concentrations. Furthermore, the resultant phosphors exhibit a small thermal quenching up to high temperature of 250°C. Therefore, the developed method is beneficial to synthesize LED phosphors of oxynitride systems at lower temperatures.     

Structure and Photoluminescence of A Blue‐Green‐Emitting Phosphor for Near‐UV White LEDs

A series of phosphors Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ have been prepared by a hightemperature solid‐state reaction using boric acid as flux. These oxyfluorides crystallize in cubic structure, space group. Under the near ultraviolet excitation within wavelength range 310–390 nm, Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ phosphors exhibit an intense emission covering a broad band of 370–500 nm derived from the 5d→4f transitions of Ce³⁺ and a characteristic emission at 544 nm of Tb³⁺. The emission can be tuned from blue to green by altering the relative ratio of Ce³⁺ to Tb³⁺ in the composition. The energy‐transfer mechanism from Ce³⁺ to Tb³⁺ is investigated based on the site occupancy of the luminescence center in the crystal structure of the Ca₁₂Al₁₄O₃₂F₂ host. More importantly, when a certain amount of boric acid is added as flux in the synthesis, the fluorescence intensity of the phosphors increases about 65%. Because of its broad excitation and efficiently tunable blue to green luminescence, the Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ phosphors may find promising application as a near UV‐convertible phosphor for white‐light‐emitting diodes.     

A Single‐Phased Sr1−y‐3x/2Al2Si2O8: xCe3+, yMn2+ with Efficient Energy Transfer as a Potential Phosphor for White‐Light‐Emitting Diodes

A series of Ce³⁺‐ and Mn²⁺‐(co‐)activated SrAl₂Si₂O₈ phosphors have been prepared at 1350°C under a reducing atmosphere and their photoluminescence properties have been studied as a function of the (co‐)dopant ions concentrations. We have discovered that energy transfer (ET) not only from Ce³⁺ to Mn²⁺ but also from “defects” to Mn²⁺ by the facts that there is existing significant overlap between the emission spectrum of Ce³⁺ (“defects”) and the excitation spectrum of Mn²⁺. The source of the “defects” in the host lattice is originated from the different charge substitution between Ce³⁺ and Sr²⁺. By adopting the principle of ET, the material SrAl₂Si₂O₈: Ce, Mn can act as a phosphor for white‐light ultraviolet light‐emitting diodes (UV‐LEDs) by tuning of the dopants contents.     

Photoluminescence Properties of Color‐Tunable Ca3La6(SiO4)6: Ce3+, Tb3+ Phosphors

A series of newly developed color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors were successfully prepared in this study. The crystal structures of the prepared phosphors were revealed to be hexagonal with space group P6₃/m, and the lattice parameters were evaluated via utilizing the Rietveld refinement method. Upon excitation at 288 nm, the emission spectra of Ce³⁺and Tb³⁺ ions co‐doped Ca₃La₆(SiO₄)₆ phosphors included a blue emission band and several emission lines. The blue emission band with a peak at 420 nm originated in the f–d transitions of Ce³⁺ ions, and the emission lines in the range of 450–650 nm were assigned to the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. Increasing the doping content of Tb³⁺ ions considerably strengthened Tb³⁺ emission and reduced Ce³⁺ emission owing to the energy transfer from Ce³⁺ to Tb³⁺ ions. The mechanism of the energy transfer was confirmed to be a dipole–dipole interaction. The effective energy transfer from Ce³⁺ to Tb³⁺ ions caused a color shift from purplish‐blue to yellowish‐green. Color‐tunable Ca₃La₆(SiO₄)₆: Ce³⁺, Tb³⁺ phosphors have the potential to be utilized in light‐emitting diodes with proper modulation of the amount of Tb³⁺ ions.     

Optical Energy Storage Properties of (Ca1−xSrx)2Si5N8: Eu2+, Tm3+ Solid Solutions

While the reddish‐orange emitting phosphors M₂Si₅N₈:Eu²⁺(M = Ca, Sr) have been intensively investigated as potential materials for white‐light‐emitting diodes, in this study, optical energy storage properties of (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ (x = 0–1) solid solutions were tuned by cation substitution, which was commonly used to tune color point for improving w‐LEDs. Partial substitution of either Ca by Sr or Sr by Ca resulted in a redshifted Eu²⁺ emission which had a demarcation point at x = 0.5. Furthermore, the (Ca_1?xSr_x)₂Si₅N₈: Eu²⁺, Tm³⁺ materials exhibited similar persistent‐ and photostimulated luminescence behaviors with a maximum intensity at about x = 0.2. Such optical energy storage characters of the samples were attributed to the more appropriate trap depths (322–333 K) and higher density of energy level traps indicated by the thermoluminescence analysis.     

Red-shift and improved afterglow of Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors via a cation substitution strategy

Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f⁶5 d¹→4f⁷ of Eu²⁺. Upon the same excitation, the B³⁺-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphors display red-shift from 609 nm to 625 nm with increasing B³⁺ concentrations. The XRD patterns show that Al³⁺ can be replaced by B³⁺ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺is rather weak, while the sample co-doped with B³⁺shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B³⁺ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B³⁺ ions caused redshift and enhanced afterglow for the Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphor.     

Partial cation substitution of tunable blue-cyan-emitting Ba2B2O5:Ce3+ for near-UV white LEDs

In this study, Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ ions act to tune the emission band to the blue-cyan region in Ba_xSr_yB₂O₅:Ce³⁺ (BSBO), Ba_xCa_zB₂O₅:Ce³⁺ (BCBO), Ba_xZn_uB₂O₅:Ce³⁺ (BZBO), and Ba_xMg_vB₂O₅:Ce³⁺ (BMBO) phosphors. A red shift occurs with the increase of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ concentration, and a blue shift occurs when the concentrations of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ exceed the critical value. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) upon 365 nm UV lamp excitation due to the crystal field splitting and centroid shifts. The excitation band shift to long wavelength by introducing ions, so that the synthesized phosphor can be better matched with the n-UV chip. The emission intensity slowly decreases with the temperature increasing. Therefore, the BMBO:Ce³⁺, BZBO:Ce³⁺, BCBO:Ce³⁺, and BSBO:Ce³⁺ phosphors with relatively good thermal stability were synthesized, which could have potential applications in the n-UV white LEDs.