Effect of Sr2+-doping on structure and luminescence properties of BaAl2Si2O8:Eu2+ phosphors

Sr²⁺ doped BaAl₂Si₂O₈:Eu²⁺ phosphor was synthesized by chemical co-precipitation method. With the increase of Sr²⁺ concentration, the phase structure of (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ changes from hexagonal phase to monoclinic phase owing to large activation energy in SrAl₂Si₂O₈ system. (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ phosphor exhibits a broad blue band peaking at 425 nm due to the 4f⁶5d–4f⁷(⁸S_7/2) transition of Eu²⁺ ions. The emission intensity increases, accompanied by the blue shift of emission maximum from 459 to 417 nm with the Sr²⁺ doping concentration increasing. The optimal concentration of Sr²⁺ ion is 40%, and the phosphor shows high color stability in CIE chromaticity diagram. The result indicates that Sr²⁺ doped phosphor not only can enhance the relative intensity but also can adjust the chromaticity coordinate.     

Synthesis and characterization of Eu2+ activated X12Al10.6Si3.4O32Cl5.4 (X=Sr,Ca) phosphors

In this article, we have reported emission characteristics of Eu²⁺ activated Sr₁₂Al_10.6Si_3.4O₃₂Cl_5.4 and Ca₁₂Al_10.6Si_3.4O₃₂Cl_5.4 phosphors, prepared by combustion synthesis. The PL excitation was monitored at two different wavelengths 254 nm (mercury excitation) and 354 nm (mercury free excitation), which shows broad-blue emission bands at 432 nm, and 438 nm for 354 nm excitation wavelength. Under mercury excitation at 254 nm it shows emission wavelengths at 470 nm, 589 nm, 592 nm, and 617 nm for the prepared Sr₁₂Al_10.6Si_3.4O₃₂Cl_5.4 and Ca₁₂Al_10.6Si_3.4O₃₂Cl_5.4 phosphors. Further it was characterized by XRD, for the investigation of phase and purity of the phosphors. Thermal degradation of the phosphors was also studied at different temperatures.     

Synthesis and luminescence properties of a broad-band red phosphor Ca3Si2O7:Eu2+ for warm white light-emitting diodes

Single-phase broad-band red-emitting Ca₃Si₂O₇:Eu²⁺ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H₃BO₃ as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu²⁺. The discussion of the results shows that Eu²⁺ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ～31 Å.     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

Photoluminescence properties of Eu2+–Mn2+ codoped Ca-α-SiAlON phosphors

Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors, Ca_0.736?ySi_9.6Al_2.4O_0.8N_15.2:0.064 Eu²⁺, yMn²⁺, were firstly synthesized by the high temperature solid state reaction method. The effects of doped Eu²⁺ and Eu²⁺–Mn²⁺ concentrations on the photoluminescence properties of the as-prepared phosphors were investigated systematically. Powder X-ray diffraction shows that pure Ca-α-SiAlON phase is synthesized after sintering at 1700 °C for 2 h under 0.5 MPa N₂ atmosphere. The excitation spectra of Eu²⁺-doped Ca-α-SiAlON phosphors are characterized by two dominant bands centered at 286 nm and 395 nm, respectively. The photoluminescent spectrum of Eu²⁺-doped Ca-α-SiAlON phosphor exhibits an intense emission band centered at 580 nm due to the allowed 4f ⁶5d→4f ⁷ transition of Eu²⁺, showing that the phosphor is a good candidate for creating white light when coupled to a blue LED chip. The intensities of both excitation and emission spectra monotonously decrease with the increment of codoped Mn²⁺ content (i.e. y value), indicating that energy transfer between Eu²⁺ and Mn²⁺ is inefficient in the case of Eu²⁺–Mn²⁺ codoped Ca-α-SiAlON phosphors.     

Potential tunable white-emitting phosphor LiSr4(BO3)3:Ce3+, Eu2+ for ultraviolet light-emitting diodes

A novel Ce³⁺/Eu²⁺ co-activated LiSr₄(BO₃)₃ phosphor has been synthesized by traditional solid-state reaction. The samples could display varied color emission from blue towards white and ultimately to yellow under the excitation of ultraviolet (UV) light with the appropriate adjustment of the relative proportion of Ce³⁺/Eu²⁺. The resonance-type energy transfer mechanism from Ce³⁺ to Eu²⁺ in LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphors is dominant by electric dipole–dipole interaction, and the critical distance is calculated to be about 29.14 Å by the spectra overlap method. White light was observed from LiSr₄(BO₃)₃:mCe³⁺, nEu²⁺ phosphors with chromaticity coordinates (0.34, 0.30) upon 350 nm excitation. The LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphor has potential applications as an UV radiation-converting phosphor for white light-emitting diodes.     

Crystal structure and photoluminescence of (Ba1−x−ySryEux)9Sc2Si6O24

Divalent europium-doped alkaline earth metal silicate phosphors, (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (x=0.005–0.1, y=0–0.95), have been successfully prepared by solid-state reaction at 1350 °C. The analysis of X-ray diffraction shows that the compounds are in a single phase at the proper concentration of Sr²⁺. At room temperature, the Eu²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor exhibits a single emission band peaking at about 506 nm. With the increasing content of Sr²⁺, the luminescent intensity of (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ weakens, and the emission peak shifts towards red. Luminescence concentration quenching occurs when Eu²⁺ content x is more than 1 mol% in (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (y=0/0.2). At low temperatures (Ba_0.9?ySr_yEu_0.1)₉Sc₂Si₆O₂₄ (y=0/0.2) phosphors have two emission bands corresponding to different Eu²⁺ crystallographic sites. The high energy peak (P₁) is quenched at room temperature, while the low energy peak (P₂) weakens much more slowly owing to the energy transfer from P₁ to P₂.     

Preparation and photoluminescence properties of the Sr1.56Ba0.4SiO4:0.04Eu2+ phosphor

The Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ phosphors were prepared via a combustion reaction and following the calcination method at low temperature. The influences of the amount of the uncommonly used SrCl₂ flux, different calcination temperatures and time on the structure and the photoluminescence (PL) properties of the phosphors were investigated. Under the excitation of 450 nm blue light, the phosphor shows the intense broad emission band from 490 nm to 650 nm, and the emission peak is centered at 553 nm. The luminescence intensity of Sr_1.56Ba_0.4SiO₄:0.04Eu²⁺ was very sensitive to the crystallinity and morphology characteristics of the phosphor. The phosphor calcined at 950 °C for 3 h in 20%H₂/80%Ar atmosphere exhibits improved PL properties due to its high crystallinity and excellent morphology characteristics. The use of the SrCl₂ flux provides a novel way to improve the crystallinity of the silicates phosphors at low preparation temperature.     

Synthesis and color-tunable luminescence properties of novel calcium aluminate silicate chloride phosphors

Eu²⁺ and Mn²⁺ co-doped calcium aluminate silicate chloride phosphors with the chemical composition of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ have been prepared by a solid-state method, and their luminescence properties have been investigated by tuning the En²⁺/Mn²⁺ ions concentration. The phase formation and microstructure of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ phosphors have been illuminated by XRD and SEM analysis. Photoluminescence (PL) spectrum reveals that Ca₃Al₂Si₂O₈Cl₄:Eu²⁺ exhibits a strong blue emission band centered at 431 nm, while Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ can emit bluish-white light by adjusting the Mn²⁺ content appropriately. The energy transfer mechanism involving Eu²⁺–Mn²⁺ have also been investigated.     

Photoluminescence characterization of a novel red-emitting phosphor In2(MoO4)3:Eu3+ for white light emitting diodes

The red-emitting phosphor In₂(MoO₄)₃:Eu³⁺ with cubic crystal structure was synthesized by a conventional solid-state reaction technique and its photoluminescence properties were investigated. The prepared phosphor can be efficiently excited by ultraviolet (395 nm) and blue (466 nm) light. The emission spectra of the phosphor manifest intensive red-emitting lines at 612 nm due to the electric dipole ⁵D₀→⁷F₂ transitions of Eu³⁺. The chromaticity coordinates of x=0.63, y=0.35 (λ_ex=395 nm) and x=0.60, y=0.38 (λ_ex=466 nm) are close to the standard of National Television Standard Committee values (NTSC) values. The concentration quenching of In₂(MoO₄)₃:Eu³⁺ is 40 mol% and the concentration self-quenching mechanism under 466 nm excitation was the dd intereaction. As a result of the strong emission intensity and good excitation, the phosphor In₂(MoO₄)₃:Eu³⁺ is regarded as a promising red-emitting conversion material for white LEDs.     

Emission-tunable phosphors Ca9MgM′ (PO4)7: Eu2+,Mn2+ (M′=Li,Na, K) for white light-emitting diodes

A series of single-composition phosphors Ca₉MgM′(PO₄)₇:xEu²⁺, yMn²⁺ (CMM′ P:Eu²⁺, Mn²⁺; M′=Li, Na, K; 0.003≤x≤0.03; 0 ≤y≤0.1) were synthesized by solid state reactions. Upon excitation at 337 nm, phosphors Ca₉MgM′ (PO₄)₇: Eu²⁺ exhibit strong blue emissions centered at 417 (Ca₉MgLi(PO₄)₇:Eu²⁺), 457 (Ca₉MgNa(PO₄)₇:Eu²⁺), and 453 (Ca₉MgK(PO₄)₇:Eu²⁺) nm respectively, which correspond to the 4f⁶5d¹→4f⁷ transitions of Eu²⁺ ions, Through an effective resonance-type energy transfer, CMM′P:Eu²⁺,Mn²⁺ phosphors exhibit a series of colors by adjusting the concentration of Mn²⁺. The result indicates that CMM′P:Eu²⁺,Mn²⁺ can be potentially used as a UV excited phosphor for white light-emitting diodes (LEDs).     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.     

Phase dependent photoluminescence and energy transfer in Ca2P2O7: Eu2+, Mn2+ phosphors for white LEDs

α- and β-Ca₂P₂O₇: Eu²⁺, Mn²⁺ phosphors were prepared by solid-state reaction. Phase transition from tetragonal (β-phase) to monoclinic (α-phase) is performed. A strong orange emission of Mn²⁺ is observed in both α-and β-Ca₂P₂O₇: Eu²⁺, Mn²⁺ upon near ultraviolet (UV) excitation through energy transfer from Eu²⁺ to Mn²⁺. The transfer efficiencies for various Mn²⁺ concentrations are estimated based on lifetime measurements of the fluorescence of Eu²⁺ in the two phases. The photoluminescence excitation spectra of α-Ca₂P₂O₇: Eu²⁺, Mn²⁺ can cover 400 nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs).     

Optical study of rare earth activated NaBa0.45Sr0.55PO4 phosphor

Dy³⁺ and Eu²⁺ activated triple phosphate NaBa_0.45Sr_0.55PO₄ phosphors were prepared by facile combustion synthesis. Excellent emission observed when NaBa_0.45Sr_0.55PO₄:Dy³⁺ and NaBa_0.45Sr_0.55PO₄:Eu²⁺ excited at 348 nm and 354 nm wavelength respectively. From a powder X-ray diffraction (XRD) analysis, the formation of compound with a trigonal–hexagonal scalenohedral structure was confirmed. In the photoluminescence spectra, the NaBa_0.45Sr_0.55PO₄:Dy³⁺ phosphor emits two distinctive colours: a blue band centred at 482 nm and a yellow band at 576 nm originating from Dy³⁺ whereas NaBa_0.45Sr_0.55PO₄:Eu²⁺ emits blue colour at 470 nm. Also, surface morphology has been studied by scanning electron microscope (SEM). Phosphors exhibit a strong absorption in the range of 340–400 nm and chromatic properties indicated that present phosphor is a hopeful candidate for near ultra violet light emitting diodes (nUV LEDs).     

Novel red phosphor of double perovskite compound La2MgTiO6:xEu3+

A novel red phosphor La₂MgTiO₆:xEu³⁺ was successfully synthesized by the conventional solid state method. Excited by ultraviolet (395 nm) and blue (465 nm) light, La₂MgTiO₆:xEu³⁺ exhibits intense red emission. Due to the lack of inversion symmetry at the doping sites, the dominant emission peak is from the transition ⁵D₀→⁷F₂. Non-radiative transitions were demonstrated to be from dipole–dipole interactions and the critical distance was estimated to be ～9.19 Å. When Eu³⁺ ions' concentration reaches 15%, the emission intensity is about three times higher than that of the conventional phosphor Y₂O₃:Eu³⁺. The Commission International de L'Eclairage chromaticity coordinate was calculated to be x=0.657 and y=0.343. All the results indicate that La₂MgTiO₆:xEu³⁺ has superior luminescence properties.     

Blue emission in Eu2+ activated MgXAl10O17 (X = Sr,Ca) phosphors

Here we reported photoluminescence properties of Eu²⁺ activated in novel and existing MgXAl₁₀O₁₇ (X = Sr, Ca) phosphor which has been prepared by combustion synthesis at 550 °C under UV and near UV excitation wavelength. The PL emission properties of MgSrAl₁₀O₁₇:Eu²⁺ were monitored at 254 nm and 354 nm respectively keeping emission wavelength at 469 nm. Whereas novel MgCaAl₁₀O₁₇:Eu²⁺ exhibit emission band at 452 nm keeping excitation at 378 nm. These blue emission corresponds to 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions. Further phosphor was analyzed by XRD for the confirmation of desired phase and purity.     

Luminescent properties of Eu2+and Dy3+ ions in Ba4Al2O7 phosphor for solid state lighting

In this paper we report the combustion synthesis of rare earth (RE=Eu, Dy) doped Ba₄Al₂O₇ phosphors. Prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), CIE color co-ordinates and their photoluminescence (PL) properties were also investigated. In case of Ba₄Al₂O₇: Eu²⁺, the emission spectra show unique band centered at 495 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺, and PL emission spectra of Dy³⁺ ion under 348 nm excitation give two bands centered at 478 nm (blue) and 575 nm (yellow), which originate from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The results indicate that the Eu²⁺ and Dy³⁺ activated Ba₄Al₂O₇ phosphor could find application in solid state lighting.     

Concentration quenching of Eu2+ in a thermal-stable yellow phosphor Ca2BO3Cl:Eu2+ for LED application

A piece-shaped phosphor Ca₂BO₃Cl: Eu²⁺ was synthesized by solid-state reaction method. This phosphor exhibited wide absorption in ultra-violet and visible range, and bright yellow emission band centering at 570 nm. The concentration quenching mechanism was verified to be a dipole–dipole interaction, and its critical transfer distance was about 17 Å by both calculated crystal structural method and experimental spectral method. This phosphor has a good thermal stability with a quenching temperature (T_1/2) of 200 °C. Yellow and white LEDs were fabricated with this phosphor and near UV chips, and the yellow LED has a high color purity of 97.0% and promising current tolerant property, while the white LED shows a luminous efficiency of 11.68 lm/W.     

Luminescent properties of Mg3Ca3(PO4)4: Eu2+ blue-emitting phosphor for white light emitting diodes

A blue-emitting phosphor, Eu²⁺-activated Mg₃Ca₃(PO₄)₄ phosphor was synthesized by conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation. Photoluminescence (PL) results showed that Mg₃Ca₃(PO₄)₄: Eu²⁺ could be efficiently excited by UV–visible light from 250 to 430 nm, which matched well with the emission wavelengths of near-UV and UV LED chips. The effects of the doped-Eu²⁺ concentration in Mg₃Ca₃(PO₄)₄: Eu²⁺ on the PL were also investigated. The result reveals that Mg₃Ca₃(PO₄)₄: Eu²⁺ is a potential blue-emitting phosphor for white LEDs.