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Red phosphors with a high quantum yield and a lower thermal quenching are needed to improve the luminescence efficiency and the stability of phosphor-converted white light-emitting diodes (pc-WLEDs). We have designed a high quantum yield NaGdSiO 4 (NGSO) based phosphor with enhanced Eu3+ emissions of the 5D 0 →7F 1 and 5D 0 →7F 2 transitions. This design is based on the Eu3+ at both the inversion and non-inversion symmetry sites. In detail, we have studied the structure, morphology, and luminescence properties of NGSO: Eu3+ phosphors. Using a 394 nm UV excitation, a series of Eu3+ emissions of 5D 0 →7F J (0–4) transitions has been observed. The internal quantum efficiency (IQE) is 83.42% and the red color purity is 91.4%. These values are much higher than some reported results. The higher IQE and double intense 5D 0 →7F 1 and 5D 0 →7F 2 emissions might originate from an unusual structure disorder around Eu3+ ions in the NGSO lattice. The lifetime of the optimal phosphor NGSO: 0.5Eu3+ is about 2 ms, suitable for solid-state lighting. The intensities of the strong emissions at 595 and 624 nm of NGSO: 0.5Eu3+ at 150 °C is about 85% of that at 30 °C, demonstrating its excellent thermal stability. Furthermore, this red NGSO: 0.5Eu3+ phosphor was packaged into a warm pc-WLED, exhibiting a lower correlated color temperature (CCT) of 4222 K and a comparable color rendering index (CRI) of 86.7. These results show that this red phosphor could act as a red component of pc-WLEDs excited by the n-UV LED chip. [ABSTRACT FROM AUTHOR]

Phosphor-converted white light-emitting diodes (pc-wLEDs) are drawing ever-increasing attention towards electronic applications. However, thermal quenching, the intensity decay with increasing temperature, presents a significant challenge for high power operation. We reverse the effect with a negative-thermal-quenching property based on energy transfer from one luminescent center to another center. The LaMgAl 11 O 19 : Er3+, Sm3+ (LMA: LaMgAl 11 O 19 : Er3+, Sm3+) phosphor has been designed, which shows a positive relationship between emission intensity and operating temperature up to 573 K (300 °C). As the temperature rises, energy transfer from Er3+ to Sm3+ occurs with higher efficiency because of stronger ionic vibration. As a result, the phosphor luminescence intensity at elevated temperatures is enhanced. Our design for negative-thermal quenching phosphor laid the foundation for the research of high-power pc-wLEDs or lasers at higher temperatures. It also has potential for wide-temperature-sensing-range radiometric optical thermometry applications. • A negative thermal-quenching phosphor LaMgAl 11 O 19 : Er3+, Sm3+ was achieved by energy transfer. • The emission intensity of the phosphor increased continuously with temperature from 298 K to 573K. • The phosphor was promising for high power wLED operations and high temperature radiometric optical thermometry. [ABSTRACT FROM AUTHOR]

The fabrication and luminescent performance of novel phosphors Na2YMg2V3O12:Dy3+ were investigated by a conventional solid-state reaction method. Under near-UV light, the Na2YMg2V3O12 host self-activated and released a broad emission band (400–700 nm, with a peak at 524 nm) ascribable to charge transfer in the (VO4)3− groups. Meanwhile, the Na2YMg2V3O12:Dy3+ phosphors emitted bright yellow light within both the broad emission band of the (VO4)3- groups and the sharp peaks of the Dy3+ ions at 490, 582, and 663 nm at a quenching concentration of 0.03 mol. The emission of the as-prepared Na2YMg2V3O12:Dy3+ phosphors remained stable at high temperatures. The obtained phosphors, commercial Y2O3:Eu3+ red phosphors, and BaMgAl10O17:Eu2+ blue phosphors were packed into a white light-emitting diode (WLED) device with a near-UV chip. The designed WLED emitted bright white light with good chromaticity coordinates (0.331, 0.361), satisfactory color rendering index (80.2), and proper correlation to a color temperature (7364 K). These results indicate the potential utility of Na2YMg2V3O12:Dy3+ phosphor as a yellow-emitting phosphor in solid-state illumination. [ABSTRACT FROM AUTHOR]

The single-component BiOCl:Dy3+ white-light-emitting phosphor was successfully prepared. The luminescence performance with excellent thermal stability indicated that this as-prepared product could act as a high-performance phosphor candidate for n-UV w-LED application. • The single-component BiOCl:Dy3+ phosphor was prepared successfully. • The phosphor emitted white light under the excitation in n-UV light region. • The PL properties obtained excellent thermal stability at higher temperatures. • The phosphor could have great potential for n-UV w-LED application. The advantages of single-component white-light-emitting phosphor make it more important for n-UV-light emitting diodes with excellent properties and efficiency. Herein, the BiOCl:Dy3+ white-light-emitting phosphor was firstly prepared by high temperature solid-state reaction. And the crystal structure, luminescence properties, lifetime, and thermal quenching behavior were carried out in detail. The results revealed that the BiOCl:Dy3+ phosphor could be excited efficiently in a broad near ultraviolet (n-UV) light region, which matched well with the n-UV chips for w-LEDs. Under the excitation at 390 nm, the BiOCl:Dy3+ phosphor exhibited white light with three emission peaks centered at 481, 575, and 664 nm, respectively. The optimal doping concentration of Dy3+ ions was found to be x = 0.03, and exchange interaction was confirmed to result in the concentration quenching. Furthermore, when the test temperature turned up to 150 °C, the intensity of emission peaks at 481 and 575 nm could still remain 77.96% and 77.93% of the initial intensity at room temperature. With the their activation energy of 0.33 eV and 0.27 eV, the excellent thermal stability of the BiOCl:Dy3+ phosphor were confirmed. All these results indicated that this as-prepared product could act as a high-performance phosphor candidate for n-UV w-LED application. [ABSTRACT FROM AUTHOR]

Emission color tunable single-phased phosphors La 7 O 6 (BO 3 )(PO 4 ) 2 : Ce 3+ , Tb 3+ , Eu 3+ were prepared by a solid state reaction method. The crystal structure, luminescence properties, energy transfer, and co-excitation behavior were investigated in detail. The La 7 O 6 (BO 3 )(PO 4 ) 2 : x Ce 3+ phosphors emit blue light under the excitation at 228 nm, corresponding to the broad 4f-5d transition of Ce 3+ . Concentration quenching phenomenon was observed when the Ce 3+ ion was x = 0.01. By co-doping the Eu 3+ and Tb 3+ ions into La 7 O 6 (BO 3 )(PO 4 ) 2 : Ce 3+ phosphors, the emission color can be tunable from blue to reddish, and then to white. The energy transfer from Ce 3+ to Eu 3+ and the co-excitation of Ce 3+ and Tb 3+ have been investigated and discussed. The color coordinate for the La 7 O 6 (BO 3 )(PO 4 ) 2 : 0.01Ce 3+ , 0.05Tb 3+ , 0.05Eu 3+ phosphor is calculated to be (0.3008, 0.3381). [ABSTRACT FROM AUTHOR]

The constructed high-efficient cyan-emitting phosphors establish a bifunctional platform involving high-color-quality lighting and anti-counterfeiting application. [Display omitted] • Ca 8 ZnY(PO 4) 7 :Eu2+ phosphors exhibited a broad cyan-emitting spectra (FWHM = 78 nm). • The quantum yield of Ca 8 ZnY(PO 4) 7 :Eu2+ phosphor is as high as 72.11 %. • The CRI value of warm w -LED devices was greatly enhanced from 83.9 to 90.5. • The transparent anticounterfeiting film held great potentials in packaging field. Constructing the broad-band emitting luminescent materials with high quantum yield is of great significance towards their widespread applications. Herein, series of Eu2+ activated, whitlockite-type Ca 8 ZnY(PO 4) 7 phosphors are developed towards bifunctional platform involving the white LED and anti-counterfeiting field. Benefiting from the typical 5d-4f transitions among Eu2+ ions, the broad asymmetric cyan-emission spectra (FWHM = 78 nm) is generated under 365 nm excitation with a highest quantum yield of ∼72.11 %. The optimal doping concentration of Eu2+ ions in the Ca 8 ZnY(PO 4) 7 host is determined as 4 % and the concentration quenching mechanism is mainly attributed to a dipole–dipole interaction. Impressively, after exploiting the newly discovered cyan-emitting phosphors Ca 8 ZnY(PO 4) 7 :Eu2+, the CRI value of as-prepared warm w -LED devices is remarkably enhanced from 83.9 to 90.5. Moreover, the w -LED exhibits an applicable correlated color temperature (CCT = 4176 K) and good color stability. Additionally, the transparent anticounterfeiting film is fabricated based on the highly efficient phosphors and soluble PVA, which presents anticounterfeiting performances due to their bright cyan emission upon UV light. Notably, their sustainability, excellent flexibility and foldability provide more possibilities applied for anticounterfeiting field. These results suggest the highly efficient phosphors Ca 8 ZnY(PO 4) 7 :Eu2+ are promising bifunctional luminescent platforms, for both high-color-quality lighting and anticounterfeiting applications. [ABSTRACT FROM AUTHOR]

A series of apatite-type phosphors Ba 4.97− x Sr x (PO 4 ) 3 Cl:Eu 2+ ( x = 0, 0.5, 1.0, 1.5, 2.0) were synthesized by the high temperature solid-state reaction method, and its luminescence properties were investigated in detail. It can be found that a red shift of the emission peak wavelength emerged from 439 to 462 nm with the continuous introduction of Sr 2+ into the crystal lattice which has been simulated by a crystal-field model. The red shift is explained by the distortion in the crystal structure through X-ray diffraction and the Rietveld refinement analysis. According to a recently raised structural model, Eu 2+ ions are surrounded by O atoms, PO 4 tetrahedrons and Ba/Sr ions. After introducing Sr 2+ into the lattice, the interatomic distance between Ba/Sr atoms and Eu 2+ was expected to become shorter, resulting in a distortion of the inner EuO n polyhedrons. Then the crystal field strength surrounding Eu 2+ was increased, finally resulting in the red shift. [ABSTRACT FROM AUTHOR]

Na 3 Gd(PO 4) 2 : Dy3+, Eu3+ phosphors were obtained by the co-doping of Dy3+ and Eu3+, and the red light emitted by Eu3+ solved the issue of high CCT due to the lack of a red-light band in the emission spectra of Dy3+. The CIE coordinate of the Dy3+and Eu3+co-doped Na 3 Gd(PO 4) 2 phosphors is calculated as (0.3442, 0.3320), which is located in the white region. The excellent thermal stability further indicated that the phosphors have great potential for applications in UV/NUV excited w-LEDs. [Display omitted] In this study, novel Na 3 Gd(PO 4) 2 :Dy3+, Eu3+ phosphors were synthesized by a high-temperature solid-state method. Single-phase white lighting-emitting Na 3 Gd(PO 4) 2 :Dy3+ phosphors exhibited blue and yellow emissions under 350 nm excitation, respectively. Eu3+-doped phosphors exhibited strong red emission at 621 nm under 394 nm excitation. Compared with that of Na 3 Gd(PO 4) 2 :Dy3+, the color rendering index of Na 3 Gd(PO 4) 2 :Dy3+, Eu3+ phosphor is improved from 74.7 to 78.9. Moreover, the correlated color temperature of Na 3 Gd(PO 4) 2 :Dy3+, Eu3+ reduced significantly from 9872 K to 5460 K. The maximum energy transfer from Dy3+ to Eu3+ in Na 3 Gd(PO 4) 2 :Dy3+, Eu3+ phosphor was ∼ 76.2% at Eu3+ concentration of 0.1. The chromaticity coordinate of the Dy3+ and Eu3+co-doped Na 3 Gd(PO 4) 2 phosphor was calculated as (0.3442, 0.3320), which is located in the white region. Furthermore, temperature-dependent photoluminescence emission properties indicate that the prepared phosphors exhibit good thermal stability. The study results indicate that the Na 3 Gd(PO 4) 2 :Dy3+, Eu3+ phosphors exhibit immense potential for ultraviolet/near-ultraviolet light-excited white light emitting diodes applications. [ABSTRACT FROM AUTHOR]

SrIn2O4, which shows lower phonon energy than CaIn2O4, is not only a good photocatalyst but also can be an excellent up-conversion (UC) host to exhibits UC luminescence. In this work, Yb3+ and/or Er3+ doped SrIn2O4 phosphors were synthesized, and their UC luminescence properties were studied and compared with those in the CaIn2O4 host. The structure of SrIn2O4: 0.01Er3+ and SrIn2O4: 0.1Yb3+/0.01Er3+ samples were refined by the Rietveld method and found to that SrIn2O4: 0.1Yb3+/0.01Er3+ showed increasing unit cell parameters and cell volume, indicating In3+ sites were substituted successfully by Yb3+ and/or Er3+ ions. From the UC luminescence spectra and diffuse reflection spectra, Er3+-doped SrIn2O4 showed very weak luminescence due to ground state absorption of Er3+; Yb3+/Er3+ codoped SrIn2O4 presented strong green (550 nm) and red (663 nm) UC emissions which were assigned to energy transfer from Yb3+ transition 2F7/2→2F5/2 to the Er3+ transition 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2. Comparing with CaIn2O4, Yb3+/Er3+ codoped SrIn2O4 showed obvious advantages with higher UC luminescent intensity. The pumping powers study showed that UC emissions in Yb3+/Er3+ codoped SrIn2O4 were attributed to energy transfer of Yb3+→Er3+ with a two-photon process. The possible UC luminescent mechanism of Yb3+/Er3+-doped SrIn2O4 was discussed. [ABSTRACT FROM AUTHOR]

Novel LaMgAl 11 O 19 :Pr 3+ phosphors for blue light pumped white light emitting diodes (w-LEDs) were prepared via a solid state reaction. The structure and luminescence properties were investigated. The LaMgAl 11 O 19 :Pr 3+ phosphors emitted a yellow light under excitation at 446 nm, which contains a green emission band, a red emission band, and a weak near infrared emission band. Concentration quenching, due to non-radiative energy transfer between Pr 3+ ions via the exchange interaction was observed when the Pr 3+ ion concentration was 0.1 mol. The colour coordinate for the yellow LaMgAl 11 O 19 :0.1Pr 3+ phosphor was calculated to be (0.4497, 0.5306). These results indicate that the LaMgAl 11 O 19 :0.1Pr 3+ phosphor can be combined with blue LED chips and can be widely used in w-LEDs application. [ABSTRACT FROM AUTHOR]

Novel LaMgAl11O19:Tm3+, Dy3+ phosphors were prepared utilizing a high-temperature solid-state reaction method. The phase formation, luminescence properties, energy-transfer mechanism from the Tm3+ to the Dy3+ ions, the thermal stability, and CIE coordinates were investigated. When excited at 359 nm, the LaMgAl11O19: xTm3+ phosphors exhibit strong blue emission bands at 455 nm. After codoping with Dy3+ and excitation at 359 nm, the LaMgAl11O19:0.03Tm3+, yDy3+ phosphors emitted white light consisting of the characteristic emission peaks of Tm3+ and Dy3+. The Dy3+ emission intensity increased with the Dy3+ concentration due to the energy transfer from Tm3+ to Dy3+, and concentration quenching due to the high Dy3+ doping concentration (y = 0.1 mol) did not occur. The calculation of the CIE coordinates of the LaMgAl11O19: Tm3+, yDy3+ phosphors revealed the tunability of the emission color from blue to bluish-white and to white by changing the excitation wavelength and the doping concentration. An energy transfer from Tm3+ to Dy3+ by dipole-dipole interaction was confirmed by the decay curve, lifetime, and energy-transfer efficiency measurements. When excited at 359 nm, the LaMgAl11O19:Tm3+, Dy3+ phosphor also showed good thermal stability, suggesting that it can be used in white LEDs excited by a GaN-based ultraviolet LED. [ABSTRACT FROM AUTHOR]

An orange reddish emitting phosphor, LaMgAl 11 O 19 :Sm 3+ , was synthesized by a high temperature solid-state reaction, and the phase formation, crystal structure and luminescence properties were investigated respectively. The LaMgAl 11 O 19 :Sm 3+ phosphor presents a highly intense orange reddish emission peak under the near ultraviolet excitation at 403 nm, which is corresponds to the 4 G 5/2 → 6 H J ( J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm 3+ ions. It was found that the dipole–dipole interactions mainly results in the concentration quenching in the LaMgAl 11 O 19 :Sm 3+ phosphor with a critical quenching concentration at about 5 mol%. The temperature dependence of luminescence properties was studied from 25 to 200 °C and indicated that LaMgAl 11 O 19 :0.05Sm 3+ phosphors had a relatively higher quenching temperature. The chromatic properties of LaMgAl 11 O 19 :0.05Sm 3+ phosphor have been found to have chromaticity coordinate of (0.578, 0.420). All these properties indicate that the orange reddish emitting LaMgAl 11 O 19 :Sm 3+ phosphor has a potential application in w-LEDs. [ABSTRACT FROM AUTHOR]

Nitrided LaMgAl11O19 phosphors were prepared by a two-step method involving synthesis at 1550°C for 4h, trituration, and firing at 1650°C for 5h under a nitrogen atmosphere. Nitrogen was doped into LaMgAl11O19 and bonded with aluminium atoms. The nitrided LaMgAl11O19 phosphors showed plate-like morphology with a rough surface and exhibited strong blue emission at 442nm and 450nm, which may be attributed to the energy transition between defect levels. A weak emission band at 590nm was ascribed to the transition between the VAl acceptor and the valence band, which was excited at 254nm. [ABSTRACT FROM AUTHOR]

Abstract: The LaMgAl11O19:Dy3+ phosphors were prepared by the high-temperature solid-state reaction method. The phase structure, luminescence properties, and the thermal stability of the phosphors were investigated. Under the excitation of 349nm, the LaMgAl11O19:Dy3+ phosphors exhibited three emission peaks at 475nm, 570nm, and 664nm, which respectively corresponded to the 4F9/2→6H15/2, 4F9/2→6H15/2, and 4F9/2→6H11/2 transitions. It was proved that dipole–dipole interaction resulted in the concentration quenching with a quenching concentration of 0.1mol. The emission intensity at 150°C was stronger than that at 25°C, indicating the good thermal stability of LaMgAl11O19:Dy3+ phosphors. The CIE coordinates of LaMgAl11O19:Dy3+ phosphors are very close to the white light coordinates (x=0.3333 and y=0.3333). Therefore, LaMgAl11O19:Dy3+ phosphor is a promising single-phase phosphor for white light emitting diodes. [Copyright &y& Elsevier]

Advances in solid-state white-light-emitting diodes (WLEDs) necessitate the urgent development of highly efficient single-phase phosphors with tunable photoluminescence properties. Herein, the Tm3+, Dy3+, and Sm3+ ions are incorporated into the orthorhombic NaGdTiO4 (NGT) phosphors, resulting in phosphors that fulfill the aforementioned requirement. The emission spectrum of Tm3+ ions overlaps well with the adsorption spectra of both Dy3+ and Sm3+ ions. Under the excitation at 358 nm, the single-phase NaGdTiO4: Tm3+, Dy3+, Sm3+ phosphor exhibits tunable emission peaks in the blue, yellow, and red regions simultaneously, resulting in an intense white-light emission. The coexisting energy transfer behaviors from Tm3+ to Dy3+ and Sm3+ ions and the energy transfer from Dy3+ to Sm3+ ions are demonstrated to be responsible for this phenomenon. The phosphors with multiple energy transfers enable the development of single-phase white-light-emitting phosphors for phosphor-converted WLEDs. [ABSTRACT FROM AUTHOR]

Rare earth aluminate phosphors are well-known for being nontoxic and environmentally friendly. In this work, Tb3+-doped SrLaAlO 4 phosphors were synthesized via a facile high temperature solid-state reaction method. The Optimum reaction temperature is determined to be 1300 °C based on the results of powder X-ray diffraction (XRD). The SEM patterns and TEM images correspond with the results of Rietveld refinement and show that the SrLa 1-x AlO 4 :xTb3+ samples present a flaky structure. The results of photoluminescence spectrums (PL) show that SrLa 1-x AlO 4 :xTb3+ phosphors can absorb in the UV–vis spectral region of 228 nm–263 nm and exhibit several emission peaks between 450 and 650 nm, and the highest peak was at 508 nm. The luminescence properties of SrLa 1-x AlO 4 :xTb3+ have a strict dependence on the cation substitution levels. When the doping concentration of Tb3+ was 0.05, the emission intensity of the sample is strongest. The thermal quenching result of the SrLa 0.95 AlO 4 :0.05 Tb3+ phosphors shows that these phosphors are relatively sensitive to temperature changes under an excitation of 228 nm, as the temperature increases from 25 °C to 125 °C, the emission intensity (peak at 548 nm) decayed to 55.11% of that at room temperature. However, when the temperature increases to 125 °C, the emission intensity (peak at 548 nm) decayed to 61.16% of the initial value under an excitation of 263 nm, which showed a relatively good thermal stability. The internal quantum efficiency (QE) values of the SrLa 0.95 AlO 4 :0.05 Tb3+ phosphors was measured and determined to be 48%. Under excitations of 228 nm and 263 nm, the lifetimes of the optimized sample SrLa 0.95 AlO 4 :0.05 Tb3+ were 1.3986 ms and 1.2095 ms, respectively, and the CIE coordinates of the sample were calculated as (0.2971, 0.4981), (0.3056, 0.5329), respectively. Under both excitations SrLa 0.95 AlO 4 :0.05 Tb3+ exhibited high-color-purity green emission. • The5D 4.→7F J (J = 6, 5, 4, 3) transitions and 5D 3 →7F J (J = 6, 5, 4) transitions of Tb3+ under UV excitation. • Dexter's theory to explain concentration quenching effect. • The fluorescence decay behavior of the SrLaAlO 4 : Tb3+ phosphor. • The research of the thermal quenching of the SrLaAlO 4 : Tb3+ phosphor. • Distribution of element in SrLaAlO 4 : Tb3+ phosphor investigated by TEM mapping. [ABSTRACT FROM AUTHOR]