Effects of Eu3+ doping on the luminescence properties of novel Sr2CaLa(VO4)3 from partial substitution of Sr2+ by Ca2+ in Sr3La(VO4)3

Eu³⁺-activated Sr_3−xCa_xLa(VO₄)₃ phosphors were fabricated via citric-acid-assisted sol combustion. Characterization of the Sr_3−xCa_xLa(VO₄)₃:Eu³⁺ samples with different concentrations of Ca²⁺ revealed a hexagonal crystal structure belonging to the R-3m space group. The amount of Ca²⁺ added (x) was controlled within 0 ≤ x ≤ 2 to yield high-purity phosphors. Scanning electron microscopy results showed that an increase in Ca²⁺ concentration resulted in a decrease in the particle size of Sr_3−xCa_xLa(VO₄)₃:Eu³⁺, with the shape gradually changing from nearly equiaxed to lath-shaped. The Sr₂CaLa(VO₄)₃:Eu³⁺ phosphor (denoted as SCLVO:Eu³⁺) exhibited the strongest photoluminescence (PL) intensity at 618 nm among the samples under excitation of 394-nm near-UV (NUV) light. The study of Eu³⁺ doping concentration confirmed that Eu³⁺ could enter the lattice of the SCLVO matrix without altering its crystal structure. SCLVO:Eu³⁺ was found to strongly absorb 394 nm NUV light and 464 nm blue light. The optimal concentration of the Eu³⁺ dopant in the SCLVO host was 0.11, which resulted in the phosphor achieving an excellent PL intensity and a color purity of 98.68%. Tunable luminescence from the orange area (0.5280, 0.4522) of Commission Internationale de l'éclairage (CIE) to the red area (0.6313, 0.3650) was achieved by adjusting the concentration of Eu³⁺. Under 394 nm excitation, SCLVO:0.11Eu³⁺ phosphor has a quantum yield (QY) of 28.2% and excellent thermal stability with 0.383 eV activation energy. Consequently, White-light-emitting diode (WLED) based on SCLVO:0.11Eu³⁺ phosphor yielded a high color rendering index (CRI), low correlated color temperature (CCT), and CIE coordinates of 91.8, 5196 K, and (0.3407, 0.3612), respectively, under the 20 mA driven current. These results indicated the tremendous potential of SCLVO:0.11Eu³⁺ phosphors for application in WLEDs excited by NUV or blue light.     

Synthesis and luminescence properties of reddish-orange-emitting Ca2GdNbO6:Sm3+ phosphors with good thermal stability for high CRI white applications

Novel reddish-orange-emitting Ca₂GdNbO₆:Sm³⁺ phosphors based on the emission of ⁴G_5/2 → ⁶H_9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm³⁺ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca₂GdNbO₆ host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca₂GdNbO₆:Sm³⁺ phosphors can be applied in high CRI white communication and flexible display applications.     

A novel red-emitting Na5W3O9F5:Eu3+ phosphor with high color purity for blue-based WLEDs

Red phosphor plays a key role in improving the lighting and display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). Meanwhile, developing new luminescent matrix materials can positively contribute to the acquisition of ideal and efficient phosphors. In this work, we propose a novel red-emitting Na₅W₃O₉F₅:Eu³⁺ (NWOF:Eu³⁺) phosphor. The phase composition, morphology, electronic structure and photoluminescence properties of the NWOF:Eu³⁺ phosphor were systematically investigated. The EXAFS results prove that the Eu³⁺ dopants occupy the Na2 and Na3 sites in the NWOF host. Under 466 nm blue light excitation, NWOF:xEu³⁺ (0.05 ≤ x ≤ 0.25) phosphors display a dominant red emission at 607 nm and achieves a high color purity (97.44%) due to the dominant electric dipole transition (⁵D₀→⁷F₂) of Eu³⁺ ions. Impressively, this red-emitting NWOF:0.25Eu³⁺ phosphor exhibits relatively superior thermal stability (450 K, >50%) and excellent chromaticity stability (2.32 × 10^?4 ≤ ΔE ≤ 6.23 × 10^?3) from 298 K to 498 K. The activation energy for thermal quenching effect is determined to be 0.22 eV. Moreover, the pc-WLED was fabricated by coupling a 460 nm blue chip with the as-synthesized NWOF:0.25Eu³⁺ red phosphor and commercial YAG:Ce³⁺ phosphor. The optical parameters of the as-fabricated pc-WLED are also measured, and the CIE coordinates remain almost constant as the drive current increases from 20 mA to 120 mA. These results indicate that the NWOF:0.25Eu³⁺ red phosphors should be a suitable candidate as a red component for the preparation of pc-WLEDs.     

A novel Eu2+/Tb3+ co-doped phosphor with pyroxene structure applied for cryogenic thermometric sensing

Pyroxene-type phosphors were widely developed due to the advantages of high chemical stability, luminous efficiency, and low production cost. In this contribution, a series of Eu²⁺/Tb³⁺ co-doped Ca_0.75Sr_0.2Mg_1.05Si₂O₆ (CSMS) phosphors with pyroxene structure were successfully synthesized by the solid-state method. Under the 340 nm excitation, the emission peaks of the phosphor show a redshift with the increase of Eu²⁺ concentration. The emitting color of Eu²⁺/Tb³⁺ co-doped samples shows a redshift attributed to the energy transfer from Eu²⁺ to Tb³⁺. Simultaneously, acquired thermometer exposes superbly temperature-sensitive properties (S_a and S_r having maximum values 4.7% K⁻¹ and 0.6% K⁻¹, respectively) over the cryogenic temperature range (77–280 K). Furthermore, it has good stability and precision at cryogenic temperatures, indicating that CSMS:0.03Eu²⁺/0.03Tb³⁺ phosphor is a very promising fluorescent material suitable for cryogenic temperature sensing.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

The composition engineering of red-emitting Eu3+-doped Ca10.5(PO4)7-type solid solution phosphors and application in LED

In this work, using Ca_10.5(PO₄)₇ as the structural model, a number of Eu³⁺-doped [Ca₉Na_3xY_1-x(PO₄)₇ (CNYP-I, 0 ≤ x ≤ 1/2) ← Ca_10.5(PO₄)₇ → Ca_9+yNa_3/2-y/2Y_(1-y)/2(PO₄)₇ (CNYP-II, 0 ≤ y ≤ 1)] phosphors were designed and synthesized through the heterovalent substitution of Y³⁺ and Na⁺ to Ca²⁺. The substitution mechanism, composition structure, luminescence performance, and thermal stability of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) as well as the solid solutions of CNYP-II (0 ≤ y ≤ 1), were discussed in detail. The morphology and element composition of CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) solid solutions were analyzed by SEM and EDS. The PL spectra of the specimens were containing the predominant red peak of emission at 612 nm caused via the transition of ⁵D₀-⁷F₂, indicating that Eu³⁺ occupies the low-symmetry center. Moreover, the site symmetry Eu³⁺ occupied changed with the x/y value. The luminous intensity of Eu³⁺-doped CNYP-I (0 ≤ x ≤ 1/2) and CNYP-II (0 ≤ y ≤ 1) phosphors at 150°C maintained about 60% of room temperature. The representative compound CNYP-I (x = 1/3) was used as the red phosphor to prepare a near-UV based white LEDs along with Ra of 80.9 and CCT of 4100 K.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

Thermal stability and luminescence of novel garnet-type yafsoanite Ca3Zn3(TeO6)2:Sm3+ phosphors for white LEDs

In this study, novel garnet-type yafsoanite tellurate Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphors are successfully synthesized using the traditional high-temperature solid-state reaction. The phase purity of the obtained phosphors is analyzed by X-ray diffraction and Rietveld refinement studies. Morphological variations are also observed with the different concentrations of Sm³⁺ ions substitution, which is analyzed using Scanning Electron Microscopy (SEM). The photoluminescent properties of the phosphors are systematically investigated. Results show that the samples display the strongest emission peak at 612 nm under the near-ultraviolet (n-UV) 409 nm excitation. This peak can be ascribed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphor shows a high color purity, exhibits excellent thermal stability and good color drifting resistance. Furthermore, red and white light-emitting diodes have been successfully prepared. The white light-emitting diodes (w-LEDs) demonstrates a high color rendering index (CRI, R_a) and low correlated color temperature (CCT). This study introduces a new orange-red-emitting phosphor and discusses its application in herb-growth w-LEDs.     

Cross Relaxation of Sm3+ and Energy Transfer Between Sm3+ and Eu3+ Ions in (Ca0.97Sr0.03)3(VO4)2 Phosphor Host

An attempt was made to verify that the inhibition of Sm³⁺→Eu³⁺ energy transfer in (Ca_0.97Sr_0.03)_2.82(VO₄)₂:Sm³⁺,0.12Eu³⁺ phosphors at Sm³⁺ content levels of >0.06 mol can be ascribed to the cross‐relaxation effect. The emission peak at around 951 nm attributed to the ⁶F_11/2→⁶H_5/2 transition of Sm³⁺, which should be barely detectable according to the energy‐gap law, was observed in this work by exciting the ⁴K_11/2 state of Sm^3 + . The results indicate that cross‐relaxation channels, which can depopulate the ⁴F_3/2 state of Sm³⁺, such as 1st Sm³⁺ (⁴F_3/2) + 2nd Sm³⁺ (⁶H_5/2)→1st Sm³⁺ (⁶F_11/2) + 2nd Sm³⁺ (⁶F_5/2) and 1st Sm³⁺ (⁴F_3/2) + 2nd Sm³⁺ (⁶H_5/2)→1st Sm³⁺ (⁶F_5/2) + 2nd Sm³⁺ (⁶F_11/2), may form and become efficient at an Sm³⁺ doping level of ≧0.06 mol. It was found that the 951‐nm emission suffered from concentration quenching, which resulted from a dipole–dipole multipolar interaction.     

Potential red-emitting NaGd(MO4)2:R (M=W,Mo, R=Eu,Sm, Bi) phosphors for white light emitting diodes applications

NaGd(MO₄)₂:R (M=W, Mo, R=Eu³⁺, Sm³⁺, Bi³⁺) phosphors were synthesized by solid-state reaction. The structure and photoluminescence properties of the samples were characterized using X-ray powder diffraction and fluorescence spectrophotometry. The ⁵D₀→⁷F₂ transition of Eu³⁺, which led to a red emission of the phosphors, was dominantly observed in the photoluminescence spectra. The doped Bi³⁺ and Sm³⁺ efficiently sensitized the emission of Eu³⁺ and effectively extended and strengthened the absorption of near-UV light with wavelengths ranging from 395 to 405 nm. In addition, energy transfers from Bi³⁺ to Eu³⁺ and from Sm³⁺ to Eu³⁺ occurred. The chromaticity coordinates of the obtained phosphors were close to the standard values of the National Television Standard Committee (x=0.670, y=0.330). The results suggest that NaGd(WO₄)_2−y(MoO₄)_y:Eu³⁺, Sm³⁺, Bi³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

Improving the luminescence properties and powder morphologies of red-emitting Sr0.8Ca0.19AlSiN3:0.01Eu2+ phosphors for high CRIs white LEDs by adding fluxes

Red-emitting Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphor with halide fluxes for use in the production of white light-emitting diodes (white LEDs) with high-colour rendering indices (CRIs) was prepared through the high-temperature solid-state method. Fluoride (NaF, SrF₂, BaF₂, CaF₂, AlF₃·3H₂O and CeF₃), chloride (NH₄Cl, BaCl₂, MgCl₂, NaCl and LiCl) and composite fluxes (NaF + SrF₂, SrF₂+NH₄Cl and NaF + NH₄Cl) were applied in the phosphors. NaF, SrF₂, NH₄Cl and NaF + SrF₂ fluxes had prominent effects on the characteristics of Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphors. Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ phosphors with various powder morphologies can be obtained through the addition of fluxes, which are conducive for phosphor formation. The powder morphologies of phosphors incorporated with NaF + SrF₂ were preferable to those of powders incorporated with other fluxes. This result indicated that the incorporation of NaF + SrF₂ into Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺ yielded phosphors with high luminescent intensity and quantum efficiency, excellent thermal stability, narrow full widths at half-maximum (FWHM, 75.2 nm), uniform rod-like morphologies with large particle sizes (D₅₀ = 16.99 μm) and good particle dispersion. White LEDs with high CRIs were obtained by combining prepared phosphors (NaF + SrF₂ additive) with the commercial green-emitting phosphors Y₃(Al,Ga)₅O₁₂:Ce³⁺ and (Sr,Ba)₂SiO₄:Eu²⁺. White LEDs with Y₃(Al,Ga)₅O₁₂:Ce³⁺ and (Sr,Ba)₂SiO₄:Eu²⁺ phosphors had correlated colour temperatures (CCTs) of 3064 and 3023 K, respectively, and CRIs of 81.8 and 92.4, respectively. Therefore, NaF + SrF₂ can be used as a favourable flux for the production of Sr_0.8Ca_0.19AlSiN₃:0.01Eu²⁺.     

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.     

Abnormal thermal quenching behavior and optical properties of a novel apatite-type NaCa3Bi(PO4)3F:Sm3+ orange-red-emitting phosphor for w-LED applications

Novel apatite-type NaCa₃Bi(PO₄)₃F:xSm³⁺ (0.01 ≤ x ≤ 0.30) orange-red-light phosphors were synthesized through the solid-state method at high temperature. The crystal structure, energy band structure, density of state, phase purity, particle morphology, photoluminescence properties, thermostability, and luminescence decay of the phosphors were comprehensively characterized. When λ_ex = 404 nm, the optimal NaCa₃Bi(PO₄)₃F:0.05 S m³⁺ phosphor showed the orange-red emission (597 nm). The NaCa₃Bi(PO₄)₃F:Sm³⁺ phosphors exhibited abnormal thermal quenching properties as their emission intensity increased by about 2.57% from 300 to 380 K. Their intensity at 440 K was still 1.01-fold stronger than that at room temperature. The abnormal thermal quenching mechanisms were well explained via the coordinate configuration scheme. The thermal activation energy (E_a) was calculated to be 0.79 eV. The color purity of all the phosphors reached 99.9%. Ultimately, a white light-emitting diode (w-LED) was fabricated based on the tri-color RGB method. The color rendering index and the chromaticity coordinates of the fabricated w-LED were 89 and (0.310, 0.319), respectively. Thus, these high thermostability NaCa₃Bi(PO₄)₃F:Sm³⁺ orange-red phosphors can be potentially used in w-LED applications.     

Photoluminescence properties and thermal stability of samarium-doped barium phosphate phosphors

In this paper, Sm³⁺-doped Ca₆BaP₄O₁₇ phosphors were synthesized via a conventional solid-state reaction method. Orange-red emission was observed from these phosphors under near-ultraviolet (UV) excitation at 405 nm. The luminescence properties of the obtained phosphors were characterized. The Ca₆BaP₄O₁₇:Sm³⁺ phosphor can be efficiently excited by near-UV and blue light, and their emission spectrum consists of three emission peaks, at 567, 602, and 650 nm, respectively. The thermal stability of Ca₆BaP₄O₁₇:Sm³⁺ phosphors was investigated systematically and corresponding mechanisms were proposed. Based on the results, the as-prepared Ca₆BaP₄O₁₇:Sm³⁺ phosphors are promising orange-red-emitting phosphors for near-UV-based white light-emitting diodes.     

Preparation and luminescent modulation of KGaSiO4:Eu3+ phosphors using for multiple anti-counterfeiting

Anti-counterfeiting technology is of great significance to information security. To obtain high-quality anti-counterfeiting materials, the developments of inorganic materials are crucial. In this paper, a series KGaSiO₄:xEu³⁺ phosphors with persistent luminescence, photoluminescence, and thermochromic have been successfully prepared and the application of quadruple anti-counterfeiting is realized. The X-ray diffraction and Rietveld refinement indicate that the phosphors are pure phase. With Eu³⁺ ions doping, the structure change, site occupancies, and color-tunable phenomenon are carefully investigated. Different from another Eu³⁺ doping phosphor, the emission of KGaSiO₄:0.2% Eu³⁺ phosphor changes with the excitation light in the region of 240 nm–306 nm. The emission color can be modulated with the surrounding temperature. Surprisingly, this phosphor can emit green afterglow light, which is attributed to the different luminescent properties of the matrix and doping of Eu³⁺ ions. The series of phosphors exhibit abundant luminescent properties. Based on their wavelength dependence, concentration quenching, long afterglow, and thermochromic properties, the KGaSiO₄:xEu³⁺ phosphors can be effective materials for quadruple-modal anti-counterfeiting devices.     

SrLaNaTeO6:Eu3+ red-emitting phosphors with high luminescence efficiency and high thermal stability for high CRI white LEDs

A novel single-phase trivalent europium activated red-emitting SrLaNaTeO₆ phosphor was first synthesized in a process of traditional high-temperature solid-state. The phase purity, morphology, and spectroscopy of the prepared phosphor were analyzed. Under 395 nm excitation, the photoluminescence (PL) spectra of the SrLaNaTeO₆:Eu³⁺ products mainly contained five dominant sharp peaks. The intense red emission peak at 615 nm was the typical ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺. The optimum product of high quenching concentration was the SrLaNaTeO₆:0.90Eu³⁺, which reached a high internal quantum efficiency (IQE) of 90.6%. The SrLaNaTeO₆:0.90Eu³⁺ was estimated to have R_c of 6.57 Å and possessed high color purity of 100.0%. The phosphors exhibited excellent thermal stability and high activation energy (E_a = 0.29 eV). The prepared white light-emitting diode (WLED) had a high color rendering index (CRI) R_a of 92 and a low correlated color temperature (CCT) of 5008 K. In conclusion, the phosphors have potential as red components for WLEDs.     

Photoluminescence Properties of Heavily Eu3+‐Doped BaCa2In6O12 Phosphor for White‐Light‐Emitting Diodes

Heavily Eu³⁺‐doped BaCa₂In₆O₁₂ phosphors were prepared by conventional solid‐state reaction, and its structural properties were investigated by means of Rietveld refinement method using an X‐ray source. XRD patterns confirm the hexagonal phase of BaCa₂In₆O₁₂: Eu³⁺ phosphors. The obtained spectrum data indicate that the emission spectra of Ba_1?xEu_xCa₂In₆O₁₂ samples excited at 393 nm exhibit a series of shaped peaks assigned to the ⁵D_0,1,2,3 →⁷F_J (J = 0,1,2,3,4) transitions. Luminescence from the higher excited states, such as ⁵D₁, ⁵D₂, and ⁵D₃, were also observed even though the Eu³⁺ concentration was up to x = 0.4. More importantly, the Ba_1?xEu_xCa₂In₆O₁₂ phosphor still emits white luminescence, when the Eu³⁺ ion concentration is up to x = 0.07 before concentration quenching is observed, which shows that the phosphor is a promising single‐phase phosphor for near ultraviolet (NUV) light‐emitting diodes (LED). Furthermore, the temperature's impact on white luminescent properties was studied. Finally, a white‐light‐emitting diodes (W‐LEDs) fabricated with the Ba_0.95Eu_0.05Ca₂In₆O₁₂ phosphor incorporated with an encapsulant in ultraviolet LEDs (λ_max = 395 nm) is discussed.     

Effect of M3+ (M = Bi,Al) co-doping on the luminescence enhancement of Ca2ZnSi2O7:Sm3+ orange-red−emitting phosphors

In this paper, the luminescence properties of Ca₂ZnSi₂O₇:Sm³⁺ phosphors were improved by co-doping with M³⁺ (M = Bi, Al) via the sol-combustion method. The structure and luminescence properties of the Ca₂ZnSi₂O₇:Sm³⁺, M³⁺ samples were investigated in detail, especially the luminescence enhancement effect of Bi³⁺/Al³⁺ co-doping. XRD results indicated that moderate Bi³⁺/Al³⁺ co-doping in the host structure did not change the tetragonal structure of Ca₂ZnSi₂O₇. The series of Ca₂ZnSi₂O₇:Sm³⁺, M³⁺ phosphors could be excited by 402 nm near-ultraviolet light and several significant emission peaks were obtained at 567, 604 and 650 nm, which originated from the electron transitions of Sm³⁺ from ⁴G_5/2 to ⁶H_5/2, ⁶H_7/2 and ⁶H_9/2 levels, respectively. The luminescence intensity of Ca₂ZnSi₂O₇:Sm³⁺ was markedly enhanced through Bi³⁺/Al³⁺ co-doping, which could be explained by Al³⁺ decreasing the crystal field symmetry and greatly increasing the red luminescence intensity, and Bi³⁺ functioning as a sensitizer to increasing the luminescence intensity through energy transfer from Bi³⁺ to Sm³⁺ ions. In conclusion, the excellent Ca₂ZnSi₂O₇:Sm³⁺, M³⁺ phosphors have potential application as red phosphors in white light emitting diodes.     

Luminescent properties and energy transfer mechanism of NaGd(MoO4)2:Sm3+, Eu3+ phosphors

Sm³⁺ singly doped NaGd(MoO₄)₂ and Sm³⁺, Eu³⁺ co-doped NaGd(MoO₄)₂ phosphors by using sodium citrate as chelating agent were synthesized via hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). During the synthesis process, the Na₃Cit concentration plays a crucial role in determining the morphology and particle size of the products. The optimal doping concentration in Sm³⁺ singly doped NaGd(MoO₄)₂ phosphor was confirmed. The relevant parameters of energy transfer in the NaGd(MoO₄)₂: Sm³⁺, Eu³⁺ phosphors have been calculated based on the fluorescent dynamic analysis. Finally, on the analysis of luminescent spectra and fluorescent dynamics, the main energy transfer mechanism between Sm³⁺ and Eu³⁺ in NaGd(MoO₄)₂ phosphor is confirmed to be electric dipole-dipole interaction, and energy transfer pathway is from ⁴G_5/2 state of Sm³⁺ to ⁵D₀ state of Eu³⁺ rather than ⁵D₁ of Eu³⁺ ions.     

Tunable color emission in LaScO3:Bi3+,Tb3+,Eu3+ phosphor

LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ (x = 0 − 0.04, y = 0 − 0.05, z = 0 − 0.05) phosphors were prepared via high-temperature solid-state reaction. Phase identification and crystal structures of the LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors were investigated by X-ray diffraction (XRD). Crystal structure of phosphors was analyzed by Rietveld refinement and transmission electron microscopy (TEM). The luminescent performance of these trichromatic phosphors is investigated by diffuse reflection spectra and photoluminescence. The phenomenon of energy transfer from Bi³⁺ and Tb³⁺ to Eu³⁺ in LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors was investigated. By changing the ratio of x, y, and z, trichromatic can be obtained in the LaScO₃ host, including red, green, and blue emission with peak centered at 613, 544, and 428 nm, respectively. Therefore, two kinds of white light-emitting phosphors were obtained, LaScO₃:0.02Bi³⁺,0.05Tb³⁺,zEu³⁺ and LaScO₃:0.02Bi³⁺,0.03Eu³⁺,yTb³⁺. The energy transfer was characterized by decay times of the LaScO₃:xBi³⁺, yTb³⁺, zEu³⁺ phosphors. Moreover absolute internal QY and CIE chromatic coordinates are shown. The potential optical thermometry application of LaScO₃:Bi³⁺,Eu³⁺ was based on the temperature sensitivity of the fluorescence intensity ratio (FIR). The maximum S_a and S_r are 0.118 K⁻¹ (at 473.15 K) and 0.795% K⁻¹ (at 448.15 K), respectively. Hence, the LaScO₃:Bi³⁺,Eu³⁺ phosphor is a good material for optical temperature sensing.