Luminescence properties of SrSi2O2N2 doped with divalent rare earth ions

The optical properties of SrSi₂O₂N₂ doped with divalent Eu²⁺ and Yb²⁺ are investigated. The Eu²⁺ doped material shows efficient green emission peaking at around 540 nm that is consistent with 4f⁷→4f⁶5d transitions of Eu²⁺. Due to the high quantum yield (90%) and high quenching temperature (>500 K) of luminescence, SrSi₂O₂N₂:Eu²⁺ is a promising material for application in phosphor conversion LEDs. The Yb²⁺ luminescence is markedly different from Eu²⁺ and is characterized by a larger Stokes shift and a lower quenching temperature. The anomalous luminescence properties are ascribed to impurity trapped exciton emission. Based on temperature and time dependent luminescence measurements, a schematic energy level diagram is derived for both Eu²⁺ and Yb²⁺ relative to the valence and conduction bands of the oxonitridosilicate host material.     

Preparation and luminescent properties of BaCa2Si3O9:Eu

A blue emitting phosphor of the triclinic BaCa₂Si₃O₉:Eu²⁺ was prepared by the combustion-assisted synthesis method and an efficient blue emission ranging from the ultraviolet to visible was observed. The luminescence and crystallinity were investigated using luminescence spectrometry and X-ray diffractometry (XRD), respectively. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu²⁺ in BaCa₂Si₃O₉:Eu²⁺ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The CIE of the optimized sample Ba_0.95Ca₂Si₃O₉:Eu_0.05²⁺ was (x, y)=(0.164, 0.111). The result indicates that BaCa₂Si₃O₉:Eu²⁺ can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes (LEDs).     

Photoluminescence studies of red-emitting NaEu(WO4)2 as a near-UV or blue convertible phosphor

Sodium europium double tungstate [NaEu(WO₄)₂] phosphor was prepared by the solid-state reaction method. Its crystal structure, photoluminescence properties and thermal quenching characteristics were investigated aiming at the potential application in the field of white light-emitting diodes (LEDs). The influences of Sm doping on the photoluminescence properties of this phosphor were also studied. It is found that this phosphor can be effectively excited by 394 or 464 nm light, which nicely match the output wavelengths of near-ultraviolet (UV) or blue LED chips. Under 394 or 464 nm light excitation, this phosphor exhibits stronger emission intensity than the Y₂O₂S:Eu³⁺ or Eu²⁺-activated sulfide phosphor. The introduction of Sm³⁺ ions can broaden the excitation peaks at 394 and 464 nm of the NaEu(WO₄)₂ phosphor and significantly enhance its relative luminance under 400 and 460 nm LEDs excitation. Furthermore, the relative luminance of NaEu(WO₄)₂ phosphor shows a superior thermal stability compared with the commercially used sulfide or oxysulfide phosphor, and make it a promising red phosphor for solid-state lighting devices based on near-UV or blue LED chips.     

Synthesis and luminescence properties of Na2Ba2Si2O7:Eu2+ phosphor

Green-emitting phosphor Na₂Ba₂Si₂O₇:Eu²⁺ has been synthesized by a conventional high-temperature solid-state reaction. The phase structure and luminescence properties are characterized by the X-ray powder diffraction, diffuse reflectance spectra, photoluminescence excitation and emission spectra, temperature-dependent emission spectra, respectively. It can be efficiently excited in the wavelength range of 325–400 nm and consists of a strong broad green band centered at about 501 nm, which is ascribed to 4f⁶6s⁰5d¹ → 4f⁷6s²5d⁰ transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in the Na₂Ba₂Si₂O₇ host is about 0.8 mol % and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, and the activation energy for thermal quenching is calculated as 0.34 eV.     

Radiative properties of Eu in BaGa2S4

A photoluminescence study of the blue-green emitting BaGa₂S₄:Eu²⁺ phosphor is reported. Diffuse reflectance, excitation and emission spectra were examined with the aim to enlarge the fundamental knowledge about the emission of the Eu²⁺ rare earth ion in this lattice. The thermal dependence of the radiative properties and the influence of the Eu²⁺ concentration were investigated. The Stokes shift, the crystal field splitting and the activation energy of the thermal quenching were determined. By combining these results with data available in literature, we discussed the radiative properties of the BaAl₂S₄:Eu²⁺ blue phosphor in relation with those determined in this study for the isostructural BaGa₂S₄:Eu²⁺ phosphor.     

Luminescent properties of green- or red-emitting Eu-doped Sr3Al2O6 for LED

Eu²⁺-doped Sr₃Al₂O₆ (Sr_3−xEu_xAl₂O₆) was synthesized by a solid-state reaction under either H₂ and N₂ atmosphere or CO atmosphere. When H₂ was used as the reducing agent, the phosphor exhibited green emission under near UV excitation, while CO was used as the reducing agent, the phosphor mainly showed red emission under blue light excitation. Both emissions belong to the d-f transition of Eu²⁺ ion. The relationship between the emission wavelengths and the occupation of Eu²⁺ at different crystallographic sites was studied. The preferential substitution of Eu²⁺ into different Sr²⁺ cites at different reaction periods and the substitution rates under different atmospheres were discussed. Finally, green-emitting and red-emitting LEDs were fabricated by coating the phosphor onto near UV- or blue-emitting InGaN chips.     

Green Eu-doped Ba3Si6O12N2 phosphor for white light-emitting diodes: Synthesis, characterization and theoretical simulation

The Eu²⁺-doped Ba₃Si₆O₁₂N₂ green phosphor (Eu_xBa_3−xSi₆O₁₂N₂) was synthesized by a conventional solid state reaction method. It could be efficiently excited by UV-blue light (250-470 nm) and shows a single intense broadband emission (480-580 nm). The phosphor has a concentration quenching effect at x=0.20 and a systematic red-shift in emission wavelength with increasing Eu²⁺ concentration. High quantum efficiency and suitable excitation range make it match well with the emission of near-UV LEDs or blue LEDs. First-principles calculations indicate that Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor exhibits a direct band gap, and low band energy dispersion, leading to a high luminescence intensity. The origin of the experimental absorption peaks is clearly identified based on the analysis of the density of states (DOS) and absorption spectra. The photoluminescence properties are related to the transition between 4f levels of Eu and 5d levels of both Eu and Ba atoms. The 5d energy level of Ba plays an important role in the photoluminescence of Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor. The high quantum efficiency and long-wavelength excitation are mainly attributed to the existence of Ba atoms. Our results give a new explanation of photoluminescence properties and could direct future designation of novel phosphors for white light LED.     

Intense green/yellow emission in Ca8Zn(SiO4)4Cl2:Eu, Mn through energy transfer for blue-LED lighting

Eu²⁺ and Mn²⁺ co-doped Ca₈Zn(SiO₄)₄Cl₂ phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu²⁺ to Mn²⁺ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu²⁺ and a yellow band at 550 nm of Mn²⁺. The excitation spectra corresponding to 4f⁷-4f⁶5d transition of Eu²⁺ cover the spectral range of 370-470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu²⁺ followed by simultaneous increase of fluorescent intensity of Mn²⁺ with increasing Mn²⁺ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu²⁺ and Mn²⁺ co-doped Ca₈Mg(SiO₄)₄Cl₂ and Ca₃SiO₄Cl₂, demonstrating a potential application in phosphor converted white LEDs.     

Effects of dopant concentrations on phosphorescence properties of Eu/Dy-doped Sr3MgSi2O8

Long afterglow Sr₃MgSi₂O₈: Eu, Dy phosphor with high brightness was prepared by sintering at high temperature and weak reductive atmosphere. The luminescent properties of this photoluminescent pigment were studied systematically by investigating concentration effects. The analytical results indicated that the main emission peaks appear at 482 nm. The excitation and emission spectra of this phosphor show that both of them are broadband. This is ascribed to the 4f⁷→4f⁶5d¹ transition of Eu²⁺ in the pigment matrix, which is in good agreement with the calculated value of 470 nm, and implies that luminescent centers Eu²⁺ occupy the deca-coordinated Sr²⁺ sites with the host of Sr₃MgSi₂O₈.     

Luminescent properties of a new green emitting Eu doped CaZrSi2O7 phosphor for WLED applications

CaZrSi₂O₇ (CZS), a modification of the thortveitite family, was prepared as a polycrystalline powder material by the conventional solid-state reaction method. Structural, thermal and photoluminescence (PL) properties of the prepared material were investigated in order to evaluate its potentiality. XRD patterns confirm the monoclinic phase of CaZrSi₂O₇: Eu²⁺ phosphors.. Emissions arising from transitions between the 5d and 4f orbital gaps of Eu²⁺ are manifested in the broadband excitation and emission spectra with major peaks at 363 and 512 nm, respectively. The excitation wavelength matches well with that of the emission of the ultraviolet-light emitting diode (UV-LED). Concentration quenching occurs when the Eu²⁺ concentration is beyond 0.05 and the dipole-dipole interaction was the reason for the corresponding quenching mechanism. The temperature dependence of emission intensity of CZS: Eu²⁺ phosphor was investigated and it showed better thermal stability than the standard YAG: Ce³⁺ phosphor.     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO₃:Eu²⁺绿色发光材料.测量了Eu²⁺浓度为1mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507nm,与理论计算值符合很好;监测482nm发射峰时,对应激发光谱的峰值为287和365nm,监测507nm发射峰时,对应的激发峰为365和405nm.研究了Eu²⁺浓度对材料发射光谱的影响,结果显示,随Eu²⁺浓度的增大,蓝、绿发射峰均发生了     

Acetate reduction synthesis of Sr2Si5N8:Eu phosphor and its luminescence properties

A novel synthesis method was developed for the efficient red phosphor, Eu²⁺-activated Sr₂Si₅N₈, by employing the strontium acetate as both the reducing agent and strontium source. The phase purity of final product was strongly dependent on the heating rate of the precursors. Sr₂Si₅N₈:Eu²⁺ (2 at%) phosphor presented a broadband excitation spectrum in the range 300–500 nm, matching well with the blue emission (400/460 nm) of current InGaN light-emitting diodes (LEDs). The red emission peaking at 619 nm gave the relatively high (about 155%) intensity compared with the Y₃Al₅O₁₂ (YAG) (P46-Y3) standard phosphor. In addition, the saturated chromatic coordinates (0.638, 0.359) allowed it a promising candidate as a red phosphor in white LEDs application for illumination or display.     

Luminescent characterization of CaAl2S4:Eu powder

The photoluminescent (PL) emission and excitation behaviour of green-emitting CaAl₂S₄:Eu²⁺ powder phosphor is reported in detail. CaAl₂S₄:Eu²⁺ emission provides good CIE colour coordinates (x=0.141; y=0.721) for the green component in display applications. Powder with a dopant concentration of 8.5 mol% shows the highest luminescence efficiency. Temperature dependence of the radiative properties, such as luminescence intensity and decay time, was investigated. In particular, the Stokes shift, the mean phonon energy, the redshift, the energy of the f→d and d→f transition and the crystal field splitting of the CaAl₂S₄:Eu²⁺ emission were determined. The thermal quenching of the emission was examined.     

A potential reddish orange emitting phosphor Ca2BO3Cl:Eu for white light-emitting diodes

A series of phosphors Ca₂BO₃Cl:Eu³⁺ were synthesized by using a high-temperature solid-state reaction technique, and their UV–vis luminescence properties were investigated. The f–f transitions of Eu³⁺ in the host lattice were assigned and discussed. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (394 nm), and exhibit reddish orange emission corresponding to the ⁵D₀→⁷F_J (J=0, 1, 2) transitions of Eu³⁺. The influence of the doping concentration and charge compensators on the relative emission intensity of Eu³⁺ was investigated, and the optimum doping concentration is 0.04. The critical distance R_c was estimated to be 17.1 Å in terms of the concentration quenching data. The present study suggests that Ca₂BO₃Cl:Eu³⁺ can be a potential candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Photoluminescence of Eu in SrGa2S4

A photoluminescence (PL) study of the green-emitting SrGa₂S₄:Eu²⁺ phosphor is reported. Diffuse reflectance, excitation, and emission spectra were examined with the aim to enlarge the fundamental knowledge about the emission of the Eu²⁺ ion in this lattice. The thermal dependence of the radiative properties was investigated. In particular, the Stokes shift, the crystal field splitting and the activation energy of the thermal quenching were determined. By combining these results with the information presented in literature, we discussed the location of the Eu²⁺ levels relative to the valence and conduction bands of SrGa₂S₄.     

Green-emissive transparent BaSi2O5:Eu film phosphor on quartz glass created by a sputtering thermal diffusion process

Eu²⁺-doped BaSi₂O₅ film phosphors on quartz substrates are fabricated by radio-frequency magnetron sputtering thermal diffusion. The BaSi₂O₅: Eu²⁺ phosphor crystals have some preferred orientations that are lattice-spacing matched with the crystallized β- SiO₂ crystals, and they show pore and grain boundary-free morphology with a rod-like shape fused into the crystallized β- SiO₂ crystals. The BaSi₂O₅: Eu²⁺ film phosphor has a high transparency, with a transmittance of about 30% in visible light. The BaSi₂O₅: Eu²⁺ film phosphor shows 510 nm green emission from the f–d transition of the Eu²⁺ ions, and in particular the best sample shows a green photoluminescence brightness of about 5% of a BaSi₂O₅: Eu²⁺ powder phosphor screen. These excellences in optical properties can be explained by less optical scattering at pores or grain boundaries, and less reflection at the continuously index-changed interface.     

Ca2BO3Cl:Ce,Eu: A potential tunable yellow-white-blue-emitting phosphors for white light-emitting diodes

Polycrystalline Ca₂BO₃Cl:Ce³⁺,Eu²⁺ phosphors were synthesized by a solid-state reaction and which could display tunable color emission from blue to yellow under an ultraviolet (UV) source by adjusting the ratio of Ce³⁺ and Eu²⁺ appropriately. The mechanism of resonance-type energy transfer from Ce³⁺ to Eu²⁺ was established to be electric dipole-dipole natured, and the critical distance was estimated to be 31 Å based on the spectral overlap and concentration quenching model. A white light was obtained from Ca₂BO₃Cl:0.06Ce³⁺,0.01Eu²⁺ phosphor with chromaticity coordinates (x=0.31, y=0.29) and relative color temperature of 7330 K upon excitation with 360 nm, which is potentially a good candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

Luminescence properties of Eu in gadolinium molybdate β′-Gd2Mo3O12 phosphors

In this paper, we report the synthesis and photoluminescence (PL) properties of β′-Gd₂Mo₃O₁₂ doped with Eu³⁺ ions. The relationship between Eu³⁺ luminescence versus concentration and temperature is discussed. In order to investigate the mechanism of concentration quenching, luminescence decay curves are measured and the Inokuti–Hirayama model is used to analyze them. The activation energy for the thermal quenching is estimated by the Arrhenius fitting. The emission spectrum of β′-Gd₂Mo₃O₁₂ exhibits the strongest emission peak at 614.5 nm due to electric–dipole transition. The excitation spectrum shows several sets of lines in the range of 350–425 nm which are associated with the typical intra-configurational 4f⁶ transitions of Eu³⁺. The spectral positions of these lines match well with the emission spectra of near-UV LEDs, which makes the phosphor find a potential application for white light-emitting-diodes.     

Orange emissive Sr3Al2O5Cl2:Eu2+ phosphor for warm-white light-emitting diodes

Orange-emitting Sr₃Al₂O₅Cl₂:Eu²⁺ phosphors were synthesized by a high-temperature solid-state reaction. The excitation spectrum shows a broad band from the UV region to the blue region. The emission spectrum shows strong orange emission peaking at 610 nm, attributed to the d–f transition of the Eu²⁺ ion. By combining the Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor with 420 nm and 460 nm chips, three white light-emitting diodes (LEDs) were fabricated. The warm-white LEDs show color rendering indexes of 76, 66 and 90 with color temperatures of 2447, 3546 and 4300 K, respectively. This new phosphor exhibits the potential to act as a single host doped with Eu²⁺ phosphor for UV or blue chip excited white LEDs.     

Luminescence characteristics of Eu2+ activated Ca2SiO4 Sr2SiO4 and Ba2SiO4 phosphorsfor white LEDs

<正>This paper investigates the luminescence characteristics of Eu²⁺ activated Ca₂SiO₄,Sr₂SiO₄ and Ba₂SiO₄ phosphors. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices,and show different emission colour variation caused by substituting M²⁺ cations for smaller cations.This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence.These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes（LEDs） based on ultraviolet chip/phosphor technology.