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A high temperature solid state method was used to prepare Na3Gd(PO4)2:Eu2+,Mn2+ phosphors with good thermal stability. The phosphor shows a broadband excitation region of 250–430 nm, which can be matched with the emissions of ultraviolet (UV)/near-ultraviolet (NUV) LED chips for white light emitting diodes (w-LEDs). The energy transfer efficiency is 74.46% from the sensitizer Eu2+ ions to the activator Mn2+ ions, which enhances the intensities of the Na3Gd(PO4)2-based phosphor. In addition, by increasing the Mn2+ doping level in the phosphor, the Na3Gd(PO4)2:Eu2+,Mn2+ phosphor first shows blue light, then turns to white light, and finally emits red light under 365 nm excitation. Besides, the temperature-dependent photoluminescence measurements indicate that the prepared phosphors exhibit good thermal stability. W-LEDs fabricated by combining a 365 nm chip with the Na3Gd(PO4)2:Eu2+,Mn2+ phosphor exhibit bright white light, which has a high color rendering index (CRI) = 91.5, and a relatively low correlated color temperature (CCT) = 5198 K. Moreover, the CIE point is calculated to be at (0.3337, 0.3465), which is located in the white light region. These results indicate that the as-prepared phosphors can be considered as potential candidates for UV/NUV light-excited w-LED applications. [ABSTRACT FROM AUTHOR]

Innovative syntheses of uniform and size-controlled chlorapatite crystals need to be developed. Molten salt synthesis is a simple process, which uses low temperatures and short reaction times to obtain synthesized powders with uniform chemical composition as well as good crystal morphology and high-phase purity. In this study, a molten salt synthesis was used to prepare ClAP microcrystallites at different temperatures, reaction times, and quantities of molten salt. ClAP microcrystallites with different sizes and morphologies were obtained, and the process parameters were optimized. The phase formation and morphologies of the ClAP microcrystallites were examined by X-ray powder diffraction and scanning electron microscopy. The results determined the optimal parameters, as follows: synthesis temperature, 600 °C; reaction time, 4 h; and ClAP/molten salt ratio, 1 : 3. The reaction time and the quantity of the molten salt, as well as the growth mechanism of the ClAP microcrystallites, were proposed based on the phase formation and morphologies of ClAP synthesized at various temperatures. ClAP phosphors activated using different ions (Sb3+, Eu2+, and Tb3+) were prepared by the molten salt method at 600 °C for 4 h with a ClAP/salt ratio of 1 : 3. The as-prepared ClAP:Sb3+/Eu2+/Tb3+ phosphors exhibited a blue-green emission (470 nm), a blue emission (460 nm), and a green emission (547 nm). Their excellent photoluminescence properties indicated their potential for application in white light emitting diodes. [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]

The development of white-light-emitting diodes (w-LEDs) makes it meaningful to develop novel high-performance phosphors excited by blue light. Herein, BiOCl:Pr3+ green-yellow phosphors were prepared via a high-temperature solid-state reaction method. The crystal structure, luminescent properties, lifetime, thermal quenching behavior, and quantum yield were studied in detail. The BiOCl:Pr3+ phosphors presented several emission peaks located in green and red regions, under excitation at 453 nm. The CIE coordinates could be tuned along with the changed doping concentration with fair luminescence efficiency. The results also indicated that the optimized doping concentration of Pr3+ ions was at x = 0.0075 because of the concentration quenching behavior resulting from an intense exchange effect. When the temperature reached 150 °C, the intensity of the emission peak at 495 nm could remain at 78% of that at room temperature. The activation energy of 0.20 eV also confirmed that the BiOCl:Pr3+ phosphor exhibited good thermal stability. All these results indicate that the prepared products have potential to be used as a high-performance green-yellow-light-emitting phosphor for blue-light-based w-LEDs. [ABSTRACT FROM AUTHOR]

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]

Na 3 Gd(PO 4) 2 phosphors doped with rare-earth metal ions Ce3+ and Tb3+ were fabricated by the solid-state reaction method. Under the excitation of 340 nm light, the Ce3+-doped Na 3 Gd(PO 4) 2 phosphors exhibit a broad emission band ranging from 370 nm to 480 nm, which emitted blue light centered at 405 nm. When excited at 373 nm, the Tb3+-doped Na 3 Gd(PO 4) 2 phosphors presented a green light emission, including a strong peak located at 547 nm. In addition, both of the Na 3 Gd(PO 4) 2 : Ce3+ and Na 3 Gd(PO 4) 2 : Tb3+ phosphors showed excellent thermal stability at different temperatures, be specific in the Na 3 Gd(PO 4) 2 : Ce3+ emission intensities at 150 °C could maintain about 84 % and the Na 3 Gd(PO 4) 2 : Tb3+ could maintain about 92.9 % of those at room temperature. A prototype of the white light-emitting diodes lamp exhibiting bright white light was fabricated by using a 365 nm near-ultraviolet-emitting LED chip, combined with Na 3 Gd(PO 4) 2 : Ce3+ blue phosphors, Na 3 Gd(PO 4) 2 : Tb3+ green phosphors, and Na 3 Gd(PO 4) 2 : Eu3+ red phosphors, which produced a high color rendering index of 89.4, and a relatively low correlated color temperature of 5496 K. Moreover, the CIE point was calculated to be at (0.3332, 0.3438), locating in the white light region. These results indicate that the as-prepared phosphors can be considered as potential candidates for ultraviolet/near-ultraviolet light-excited white light-emitting diodes applications. • The Na 3 Gd(PO 4) 2 : Ce3+, Tb3+ phosphors were prepared with excellent thermal stability. • Both blue and green light phosphors have high internal quantum efficiency. • The CRI, CCT and CIE coordinate of the self-made w-LED has good performance. • The phosphors are potential for application in UV/NUV based w-LEDs. [ABSTRACT FROM AUTHOR]

Graphical abstract Na 3 GdP 2 O 8 : Sm3+ and Na 3 GdP 2 O 8 : Dy3+ phosphors were successfully prepared and emitted orange-red and white light under UV/NUV excitation, respectively. The excellent thermal stability further indicated that these phosphors have great potential for applications in UV/NUV excited w-LEDs. Highlights • The novel Sm3+ and Dy3+ ions doped Na 3 GdP 2 O 8 phosphors were prepared. • Both orange-red and white lights could obtain with excellent thermal stability. • These phosphors are potential for application in UV/NUV based w-LEDs. Abstract With the rapid demand of white light emitting diodes (w-LEDs), studies on the ultraviolet/near-ultraviolet (UV/NUV) light excited phosphors are becoming more and more important. Herein the novel Na 3 GdP 2 O 8 : Re3+ (Re = Sm, Dy) phosphors were synthesized through a high-temperature solid-state reaction method. The Sm3+-doped Na 3 GdP 2 O 8 phosphors emitted orange-red light centered at 600 nm, under the NUV excitation at 403 nm. When excited at 350 nm, the Na 3 GdP 2 O 8 : Dy3+ phosphors presented a white light emission, including three peaks at 483, 578, and 670 nm, respectively. In addition, both of the Na 3 GdP 2 O 8 : Sm3+ and Na 3 GdP 2 O 8 : Dy3+ phosphors showed excellent thermal stability at different temperatures, of which the emission intensities at 150 °C could maintain about 75% and 79% of those at room temperature, respectively. These results indicate that the as-prepared phosphors can be considered as potential candidates for applications in UV/NUV excited w-LEDs. [ABSTRACT FROM AUTHOR]

The Eu 3+ ion activated pyrochlore-type La 2 Zr 2 O 7 red emitting phosphor was prepared through solid-state reaction. The electronic structure of La 2 Zr 2 O 7 was investigated with density functional theory (DFT) calculation. The phase purity, crystalline structure, morphology and lattice parameters of the Eu 3+ ion doped La 2 Zr 2 O 7 through powder X-ray diffraction and Rietveld refinement were also elucidated in details. The as-prepared La 2 Zr 2 O 7 : Eu 3+ phosphors presented excellent red light emission with intense absorption bands in the near-ultraviolet and blue light regions. The optimized doping concentration of Eu 3+ ions was found to be 0.05 with an ideal CIE coordinate index of (0.62, 0.38). Finally, the excellent thermal stability of La 2 Zr 2 O 7 : Eu 3+ phosphor was also determined according to the temperature dependent emission spectra, excited at 393 nm. All these results indicated that the La 2 Zr 2 O 7 : Eu 3+ phosphors had high potential for applications in solid-state white light-emitting diodes as suitable red-emitting components for white light emitting diodes (w-LEDs), combined with near-ultraviolet or blue lighting chips. [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]

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]

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]

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]