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Mn4+‐activated CaAl12O19 (CAO: Mn4+) is recognized as a promising candidate for red phosphor used in wide color gamut displays. However, the spontaneous self‐reduction of Mn4+ to Mn2+ occurs for charge compensation through Mn2+‐Mn4+ substitution for Al3+‐Al3+, lowering the quantum efficiency of Mn4+. To suppress the self‐reduction, some divalent metal ions, including Ba2+, Sr2+, Cd2+, Zn2+, and Mg2+, are added for charge compensation instead of Mn2+, but only small luminescence enhancement is observed. In this paper, remarkable luminescence enhancement in CAO: Mn4+ via co‐doping Be2+ is reported. The photoluminescence properties are studied as a function of Be2+ doping concentration, and the optimal Be2+ concentration of 0.01 is found. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation, higher than those via co‐doping other divalent metal ions. This study indicates that the addition of Be2+ dominates the charge compensation because Be2+ is closer to Al3+ in size than Mn2+ and other divalent metal ions. The backlight light‐emitting diodes using CAO: Mn4+, Be2+ are fabricated, exhibiting a 110.1% Nation Television Standards Committee (NTSC) color gamut, wider than both the current commercial backlight using K2SiF6: Mn4+ (KSF) red phosphor and the conventional one using YAG yellow phosphor. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) phosphors offer a novel luminescent solution for NIR spectroscopy, but their efficiency remains low. Herein, it is demonstrated that the high transparency of a phosphor improves its external quantum efficiency by developing a new inorganic–organic composite phosphor. The new bulk‐size and highly transparent composite phosphor is fabricated through layer‐by‐layer assembly of micron‐sized hexagonal LiSrAlF6:Cr3+ powder phosphor. The inline transparency of the final bulk phosphor can be controlled from 0% to 90.2% at a large solid concentration of ≈47 vol.%. With high transparency, the new bulk phosphor allows the phosphor‐conversion light‐emitting diode (pc‐LED) a 2.9 times improvement in efficiency. This paper inspires a feasible and low energy consumption method to facilitate next‐generation NIR pc‐LED phosphors. [ABSTRACT FROM AUTHOR]

Cr3+‐activated Gd3Ga5O12 garnet (GGG:Cr3+) near‐infrared (NIR) phosphors have shown promising applications in regulating plant growth. However, the low external quantum efficiency (EQE) results in a wall‐plug efficiency (WPE) of phosphor‐converted light‐emitting diodes (pc)‐LEDs of only ≈15%. Herein, an easy strategy to improve the luminescent properties of the GGG:Cr3+ phosphor is reported. Through optimization of the synthesized technology, the EQE is enhanced to 43.6%. Remarkably, the fabricated pc‐LEDs achieve a WPE as high as 34.3%. These results demonstrate a significant advancement in the development and applications of NIR phosphor materials and NIR pc‐LED devices. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes are next‐generation smart NIR light sources. However, the NIR phosphor suffers from serious thermal quenching (TQ), resulting in efficiency reduction and spectral shift. Here, a novel strategy is realized to suppress TQ by minimizing bond angle distortion, completely different from the conventional TQ suppression approach through bond length variation. Li(Sr1−xCax)AlF6:Cr3+ NIR phosphor is taken as an example in which rotation between the two parallel fluorine planes perpendicular to the C3 axis in the [AlF6] octahedron is found to dominate TQ. Increasing x from 0 to 1 reduces the amplitude of the rotation from 16.17° to 5.06°, weakening the electron–phonon coupling and, consequently, raising the TQ temperature significantly from 320 to 570 K. This mechanism is elucidated from both theoretical calculations and spectroscopic studies. The findings open a new horizon for the exploration of thermally stable NIR phosphors. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphor converted light emitting diodes (pc‐LEDs) are novel compact light sources that enable portable devices for substance detection. However, to achieve such efficient pc‐LEDs is still a challenge due to lack of efficient phosphors. In this paper, Stokes shift as an efficiency predictor is emphasized. In Cr3+ activated Ca2LuZr2Al3O12 (CLZA) garnet phosphor, Stokes shift decreases from 2990 to 2854 cm−1 upon substituting Ca‐Zr with Lu‐Al. As a result, electron–phonon coupling related nonradiative process is reduced. The external quantum efficiency is significantly enhanced to 47.4%, and the as fabricated NIR pc‐LED offers 33.7% @10 mA electro‐optical efficiency. The results can advance the development of efficient NIR phosphors. [ABSTRACT FROM AUTHOR]

Efficient cyan phosphors are needed for filling the cyan cavity in the spectra of phosphor converted white light-emitting diodes (pc-WLEDs). In this paper, we reported a strategy to enhance the emission of cyan BaSi2O2N2:Eu2+ phosphor by adding Ho3+ to promote conversion from Eu3+ to Eu2+. External quantum efficiency reached up to 68.9%, excited by 405 nm, based on the observation of emission intensity decrease of Eu3+ and absorption enhancement of Eu2+ with addition of Ho3+. Using the luminescence-enhanced cyan phosphor, commercial yellow, and red phosphors, full-color WLEDs with high color rendering at various color temperatures were packaged on blue LED chips. A WLED with ultra-high color rendering index (CRI = 98) and high luminous efficiency (95 lm/W) at correlated color temperature of 5112 K was achieved. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphor‐converted (pc) LED is promising next‐generation tiny light source for smart and broadband NIR spectroscopy technology. However, NIR phosphors suffer from challenges in terms of low quantum efficiency and bandwidth. By selecting a host that has a big bandgap and weakening coupling effect among Cr3+, a novel LiGaP2O7:Cr3+ (LGAP:Cr3+) NIR phosphor that has a high external quantum efficiency (28.3%) is discovered. Under ≈450 nm excitation, LGAP:Cr3+ shows broad NIR emission from 700 to 1100 nm with a bandwidth of ≈170 nm. Importantly, the fabricated pcLED demonstrates bright broadband NIR light and an excellent performance in night vision. The results promise the use of the LGAP:Cr3+ phosphor for high‐performance broadband NIR LED that employs only one tiny blue LED chip. [ABSTRACT FROM AUTHOR]

Far‐red (FR) phosphor‐converted light‐emitting diodes (pc‐LEDs) driven by blue LED chips are novel light sources for applications in phototherapy, photosynthesis, natural light simulation, and so on but still bear low electricity‐to‐FR light conversion efficiency (≤ 23%) due to deficiency of phosphors that have both high blue light absorptance and high FR internal quantum efficiency (IQE) for the realization of efficient blue to FR conversion. FR Ca3Sc2Si3O12 (CSSG):Cr3+ garnet phosphor has ultra‐high IQE (> 90%) but low blue light absorption. Here, a twofold increase of blue light absorption cross‐section is reported with still high FR IQE via Lu3+−Mg2+ substitution for Ca2+−Sc3+ in CSSG:Cr3+ to form Ca3–xLuxMgxSc2–xSi3O12:Cr3+ garnet solid solution, which is attributed to enhanced mixing of odd‐parity configuration into 3d configuration of Cr3+ induced by the cations substitution. Optical properties, crystal field strengths, and thermal stabilities of the solid solution phosphors are studied as a function of x. After complete replacement of Sc3+, the as‐fabricated FR pc‐LED emits at 750 nm with 65.7% blue‐to‐FR quantum conversion efficiency and consequently offers an electricity‐to‐FR light conversion efficiency over 30%. Moreover, the solid solution phosphors show high quenching temperatures in the range of 580–610 K. The results can advance the development of efficient FR phosphors and pc‐LEDs for various applications. [ABSTRACT FROM AUTHOR]

Super broadband near‐infrared (NIR) phosphor converted light‐emitting diodes (pc‐LEDs) are future light sources in NIR spectroscopy applications such as food testing. At present, a few blue LED excitable super broadband NIR phosphors (bandwidth > 300 nm) have been developed producing the NIR output powers below 26 mW at 100 mA input current after LED packaging. Here, an efficient super broadband NIR phosphor achieved by doping Yb3+ is reported in the NIR Ca2LuZr2Al3O12:Cr3+ (CLZA:Cr3+) garnet phosphor developed previously. Benefited from the superposition of Cr3+ emission and highly efficient Yb3+ emission excited by energy transfer from Cr3+, the codoped CLZA:Cr3+,Yb3+ phosphor shows a bandwidth of 320 nm and an internal quantum efficiency of 77.2% both higher than that (150 nm and 69.1%) of singly doped CLZA:Cr3+ phosphor. The codoped phosphor converts LED produced 41.8 mW NIR output at 100 mA input current. The pc‐LED as a light source is also well applied to the NIR transmission spectra measurement of water. The results indicate the great potential of CLZA:Cr3+,Yb3+ phosphor in super broadband NIR pc‐LED applications. [ABSTRACT FROM AUTHOR]

Luminescence of Pr 3+ in Li 2 SrSiO 4 showed a broader f–f emission band compared with YAG:Pr 3+ . Atom parameters of Li 2 SrSiO 4 crystal were refined to provide data for quantifying the distortion of [SrO8] polyhedron. The distortion of [SrO8] was compared with that of [YO8] polyhedron in YAG to show the different Pr 3+ environments in Li 2 SrSiO 4 and YAG. Then, Pr 3+ was co-doped with Eu 2+ in Li 2 SrSiO 4 to provide a single phosphor for wLEDs. Energy transfer processes from 5d of Eu 2+ to both 3 P 2 and 1 D 2 of Pr 3+ were observed. The interaction type between Eu 2+ –Pr 3+ was proved to be dipole-quadrupole and kinetics of the energy transfer process was discussed based on Inokuti–Hirayama model. [ABSTRACT FROM AUTHOR]

CaO:Ce3+,Mn2+ phosphors with various Mn2+ concentrations were synthesized by a solid state reaction method. Efficient energy transfer from Ce3+ to Mn2+ was observed and it allows the emission color of CaO:Ce3+,Mn2+ to be continuously tuned from yellow (contributed by Ce3+) to red (by Mn2+) with an increase in Mn2+ concentration and upon blue light excitation. The red emission becomes dominant when the Mn2+ concentration is ≥0.014 with an energy transfer efficiency higher than 87% which can reach as high as 94% for a Mn2+ concentration of only 0.02. A critical distance of 10.5 Å for the Ce3+–Mn2+ energy transfer was determined. A faster decrease of Ce3+ luminescence intensity in comparison with its lifetime was observed on increasing the Mn2+ concentration. The analysis of this feature reveals that the Ce3+ excitation energy can be completely transferred to Mn2+ if the Ce3+–Mn2+ distance is shorter than 7.6 Å. A warm white LED was fabricated through integrating an InGaN blue LED chip and a blend of two phosphors (YAG:Ce3+ yellow phosphor and CaO:0.007Ce3+,0.014Mn2+ red phosphor) into a single package, which has CIE chromaticity coordinates of (x = 0.37, y = 0.35), a correlated color temperature of 3973 K and a color rendering index of 83.1. The results indicate that CaO:Ce3+,Mn2+ may serve as a potential red phosphor for blue LED based warm white LEDs. [ABSTRACT FROM AUTHOR]

Abstract: More recently, Ce3+ activated γ-Ca2SiO4 has been reported and it shows great potential application as a yellow-emitting phosphor for white LEDs. However, β-Ca2SiO4, another known phase of Ca2SiO4, doped with Ce3+ is not available. It is interesting to know if β-Ca2SiO4:Ce3+ can also be suitable for white LEDs. For this reason, we synthesized a series of β-Ca2SiO4:Ce3+ phosphors by solid state reaction. β-Ca2SiO4:Ce3+ exhibits an intense blue emission band peaked at 425nm with a bandwidth of 68nm which is attributed to the typical Ce3+ 4f05d1→4f1 transitions. The integral intensity of the concentration-optimized β-Ca2SiO4:Ce3+ can be as high as 71% of the commercial BAM blue phosphor upon 360nm excitation. The excitation spectra of β-Ca2SiO4:Ce3+ consist of three broad bands with maxima at 252, 289 and 348nm , which are ascribed to the 4f1→4f05d1 transitions of Ce3+. Thermal quenching property of β-Ca2SiO4:Ce3+ was evaluated and the results show that the integral PL intensity at 150°C maintains about 93% of that at room temperature. The excellent thermal stability and intense emission upon NUV light excitation suggest that β-Ca2SiO4:Ce3+ can be used as a potential blue-emitting phosphor for NUV white LEDs. [Copyright &y& Elsevier]

Abstract: A series of Ce3+ and Mn2+ co-doped Sr9Sc(PO4)7 phosphors have been synthesized by high temperature solid state reaction and their luminescence properties are investigated. The obtained phosphors exhibit a broad excitation band ranging from 240 to 350nm and two emission bands centered at about 370 and 610nm upon 310nm excitation, resulting from the 5d–4f transitions of Ce3+ and the d–d forbidden transition of Mn2+, respectively. Energy transfer mechanism from Ce3+ to Mn2+ in Sr9Sc(PO4)7 host matrix was studied and demonstrated to be a resonant type via a dipole–dipole mechanism based on the decay lifetime data. Furthermore, we have calculated the critical distance for Ce3+→Mn2+ energy transfer to be about 6.12Å by the spectral overlap method. Through effective energy transfer, a color-tunable emission varied from blue to reddish orange can be realized by adjusting the ratio of Ce3+ to Mn2+. Our results indicate the novel Sr9Sc(PO4)7: Ce3+, Mn2+ phosphor can be a promising candidate for a color-tunable phosphor applied in a UV white light emitting diodes. [Copyright &y& Elsevier]

Highlights: [•] A novel orange–red phosphor Sr9Sc(PO4)7:Eu3+ has been synthesized and investigated. [•] The phosphors can be effectively excited by near UV (394nm) light. [•] The thermal quenching temperature of Sr9Sc(PO4)7:Eu3+ is above 200°C. [ABSTRACT FROM AUTHOR]

Eu2+-Mn2+ codoped yellow-emitting Sr9Sc(PO4)7 (SSP) phosphors have been synthesized by solid-state reactions. The synthesis, structure refinement, and luminescence properties of the obtained phosphor were investigated in detail. The obtained phosphor exhibits a strong excitation band between 250 and 450 nm, matching well with the dominant emission band of a near-UV light-emitting-diode (LED) chip. Upon excitation at 365 nm, the Sr9Sc(PO4)7:Eu2+, Mn2+ phosphor shows strong yellow emissions centered at 510 and 610 nm. The energy transfer mechanism from Eu2+ to Mn2+ in Sr9Sc(PO4)7:Eu2+, Mn2+ has been studied and demonstrated to be a resonant type through a dipole-quadrupole mechanism based on the decay lifetime data. These results indicate that yellow-emitting Sr9Sc(PO4)7:Eu2+, Mn2+ can serve as a promising candidate for application in white-light LEDs. [ABSTRACT FROM AUTHOR]

Abstract: A red-emitting Gd3PO7:5% Eu3+ phosphor is reported. Through transitions of 5d→4f (7F1 and 7F2) in Eu3+, the phosphor shows a bright red emission under ultraviolet (UV) light excitation. The emission intensity at 615nm corresponding to 5D0 → 7F2 transition of Eu3+ ion depending on irradiation time under 394nm excitation increases firstly and then small reduces. After 20min for UV-light irradiation, it decreases by about 0.5% suggesting that the photostability of the red phosphor Gd3PO7:Eu3+ is excellent. Under 325nm excitation, the emission intensities grow rapidly as the temperature increases from 75K to 285K and then it keeps on growing slowly until 475K, revealing the excellent thermostability of the red phosphor Gd3PO7:Eu3+. Decay time and time-resolved luminescence measurements have also been studied. All the results reveal that Gd3PO7:Eu3+ is a promising red-emitting phosphor for UV LED applications. [Copyright &y& Elsevier]

Abstract: Non-radiative energy transfers (ET) from Ce3+ to Pr3+ in Y3Al5O12:Ce3+, Pr3+ and from Sm3+ to Eu3+ in CaMoO4:Sm3+, Eu3+ are studied based on photoluminescence spectroscopy and fluorescence decay patterns. The result indicates an electric dipole–dipole interaction that governs ET in the LED phosphors. For Ce3+ concentration of 0.01 in YAG:Ce3+, Pr3+, the rate constant and critical distance are evaluated to be 4.5×10−36 cm6 s−1 and 0.81nm, respectively. An increase in the red emission line of Pr3+ relative to the yellow emission band of Ce3+, on increasing Ce3+ concentration is observed. This behavior is attributed to the increase of spectral overlap integrals between Ce3+ emission and Pr3+ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce3+ concentration. In CaMoO4:Sm3+, Eu3+, Sm3+–Eu3+ transfer occurs from 4G5/2 of Sm3+ to 5D0 of Eu3+. The rate constant of 8.5×10−40 cm6 s−1 and the critical transfer distance of 0.89nm are evaluated. [Copyright &y& Elsevier]

Abstract: We report an intense full-color emission originating from 5D0,1,2,3 to 7F0,1,2,3,4 transitions of Eu3+ in CaSc2O4 upon 395nm excitation. The emission spectra vary with increasing Eu3+ concentration, demonstrating tunable color coordinates from white to red region in the CIE chromaticity diagram. Considering the relaxation from 5D J to 5D J −1 through cross energy transfer, the Eu3+ concentration dependent emission spectra are well simulated based on the analysis of steady state rate equations and the measured lifetimes of the 5D J levels. It is suggested that CaSc2O4:Eu3+ could be a potential single-phased full-color emitting phosphor for near-ultraviolet InGaN chip pumped white light emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: 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 400nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: A series of Eu2+-activated Sr9Sc(PO4)7 yellowish-green emitting phosphors were synthesized by conventional solid-state reaction. The photoluminescence (PL) properties and concentration quenching mechanism of the as-prepared phosphors were investigated. The emission spectrum exhibits a broad and asymmetric band peaking at 510nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The excitation spectrum exhibits a broad band extending from 250 to 450nm, which matches well with the emission of near ultraviolet (n-UV) chips (350–430nm). Non-radiative transitions between Eu2+ ions in the Sr9Sc(PO4)7 host have been demonstrated to be attributable to dipole–dipole interactions, and the critical distance was calculated to be 23.1Å. These results indicate that Sr9Sc(PO4)7:Eu2+ phosphor could serve as a promising candidate for application in n-UV white-light LEDs. [Copyright &y& Elsevier]

Eu2+singly and Eu2+, Mn2+co-doped Sr2Mg3P4O15exhibit not only the well known blue emission band of Eu2+peaking at 448 nm but also a new band at 399 nm in violet. They are attributed to Eu2+on different Sr2+sites. The Eu2+for the violet band can transfer energy to the red emitting Mn2+more efficiently than Eu2+for the blue band. The new Eu2+band could enable Sr2Mg3P4O15:Mn2+, Eu2+to be a promising phosphor for enriching the red component of white LEDs. [ABSTRACT FROM AUTHOR]

The α-Ca2P2O7:Eu2+, Mn2+ phosphors show two emission bands peaking at around 416 (blue) and 600 nm (orange), originating from the allowed f-d transition of Eu2+ and the forbidden 4T1-6A1 transition of Mn2+, respectively, under near ultraviolet (UV) excitation at 400 nm. Spectroscopy and fluorescence lifetime measurements demonstrate that energy transfer from Eu2+ to Mn2+ performs with transfer efficiency as high as 65% for Mn2+ concentration of 12 mol %. The authors have fabricated a white light emitting diode (LED) through the integration of GaN near-UV chip and two phosphor blends (α-Ca2P2O7:Eu2+, Mn2+ blue-orange phosphor and Ba2SiO4:Eu2+ green phosphor) into a single package. The white LED shows color rendering index of 78, luminescent efficiency of 9 lm/W, and low color point variation against forward-bias currents. [ABSTRACT FROM AUTHOR]

Abstract: Luminescent properties of Eu2+-doped phosphors with nominal composition of 2SrO·MgO·xSiO2 (0.8⩽x⩽1.2) are studied. The emission spectra consist of a blue band (460nm) and a yellow band (550nm), the relative intensities of which change with the SiO2 composition x. It is found that a combination of the blue and yellow bands can generate white light at x around 1 under near- ultraviolet excitation. X-ray diffraction patterns of the phosphors demonstrate both Sr3MgSi2O8 and Sr2SiO4 phases, in which Eu2+ contributes to the blue and yellow emissions, respectively. The relative intensity variation of the two bands is attributed to the relative proportion of the two phases dependent on SiO2 composition. A white light emitting diode fabricated using a GaN chip (λem=400nm) and this phosphor is obtained, exhibiting color coordinates of x=0.33, y=0.34, color rendering index of 85 and luminous efficiency of 6lm/W. [Copyright &y& Elsevier]

Broadband near‐infrared (NIR) phosphor‐converted light emitting diode (pc‐LED) is demanded for wearable biosensing devices, but it suffers from low efficiency and low radiance. This study reports a broadband NIR Ca3‐xLuxHf2Al2+xSi1−xO12:Cr3+ garnet phosphor with emission intensity enhanced by 81.5 times. Chemical unit co‐substitution of [Lu3+−Al3+] for [Ca2+−Si4+] is responsible for the luminescence enhancement and further alters the crystal structure and electronic properties of the garnet. Using the optimized phosphor, a NIR pc‐LED with photoelectric efficiencies of 21.28%@10 mA, 15.75%@100 mA and NIR output powers of 46.09 mW@100 mA, 54.29 mW@130 mA is fabricated. The high power NIR light is observed to penetrate upper arms (≈8 cm). For application in NIR spectroscopy, the NIR pc‐LED is used as light source to measure transmission spectra of water, alcohol, and bovine hemoglobin solution. These results indicate the NIR garnet phosphor to be a promising candidate for NIR pc‐LED. [ABSTRACT FROM AUTHOR]

Trivalent terbium (Tb3+)‐activated luminescence materials usually show highly efficient green emission with the full width at half maximum of merely 10 nm, but suffer from the unsatisfactory excitable wavelength (<380 nm) as well as the inefficient light absorption. Here, the realization of efficient visible light excitation of Tb3+ is demonstrated in terbium‐concentrated garnet Ca2TbHf2Al3O12 (CTHA) by introducing Ce3+ as the sensitizer. Owing to highly efficient energy transfer from Ce3+ to Tb3+, CTHA:Ce3+ combines advantages of the extra narrow green emission of Tb3+ peaking at 544 nm and the efficient broad excitation of Ce3+ covering the short‐wavelength visible light from 380 to 450 nm. The color gamut of the prototype white light‐emitting diode (LED) by using CTHA:Ce3+ as the green emitter can reach 95% (coverage ratio) of National Television Standards Committee (NTSC) space in Commission Internationale de L'Eclairage (CIE) 1931, indicating its great potential for LED (or laser diode)‐based applications. [ABSTRACT FROM AUTHOR]

Mn4+‐activated CaAl12O19 (CAO: Mn4+) is recognized as a promising candidate for red phosphor used in wide color gamut displays. However, the spontaneous self‐reduction of Mn4+ to Mn2+ occurs for charge compensation through Mn2+‐Mn4+ substitution for Al3+‐Al3+, lowering the quantum efficiency of Mn4+. To suppress the self‐reduction, some divalent metal ions, including Ba2+, Sr2+, Cd2+, Zn2+, and Mg2+, are added for charge compensation instead of Mn2+, but only small luminescence enhancement is observed. In this paper, remarkable luminescence enhancement in CAO: Mn4+ via co‐doping Be2+ is reported. The photoluminescence properties are studied as a function of Be2+ doping concentration, and the optimal Be2+ concentration of 0.01 is found. The internal quantum efficiency of 74.9% and external quantum efficiency of 56.3% are achieved under UV excitation, higher than those via co‐doping other divalent metal ions. This study indicates that the addition of Be2+ dominates the charge compensation because Be2+ is closer to Al3+ in size than Mn2+ and other divalent metal ions. The backlight light‐emitting diodes using CAO: Mn4+, Be2+ are fabricated, exhibiting a 110.1% Nation Television Standards Committee (NTSC) color gamut, wider than both the current commercial backlight using K2SiF6: Mn4+ (KSF) red phosphor and the conventional one using YAG yellow phosphor. [ABSTRACT FROM AUTHOR]

SrAlSi4N7:0.05Ce3+,xEu2+ is a highly color-tunable phosphor with emission shifting from 550 to 610 nm with increasing Eu2+ concentration. [ABSTRACT FROM AUTHOR]

Abstract: Eu3+ and Sm3+ co-doped CaMoO4 microclews have been successfully synthesized via a facile hydrothermal method directly in surfactant-free environment. The as-prepared phosphor present clew-like agglomerates composed of 40nm nanosheets under the moderated reaction temperature. The red phosphor CaMoO4:Eu3+, Sm3+ can generate a strong absorption line at 405nm, originating from 6H5/2 → 6P5/2 transition of Sm3+, which is suitable for the emission of the near-ultraviolet light-emitting diodes (∼400nm). Energy transfer between Sm3+ and Eu3+ is detected from the varied photoluminescence spectra with different Eu3+ concentrations and the energy transfer mechanism is clarified via the photoluminescence spectra. When Sm3+ is excited (405nm), the electron is excited from 6H5/2 to 6P5/2, and then relaxed to 4G5/2. It jumps from 4G5/2 to the lower levels corresponding to the emissions of Sm3+; meanwhile, the transfers from 4G5/2 state of Sm3+ ion to 5D0 state of Eu3+ ion come out. The transition of 5D1 → 7F J (J =0, 1, 2) does not appear indicating that the transfer from 4G5/2 state of Sm3+ to 5D0 state rather than 5D1 state of Eu3+ is the energy transfer pathway. [Copyright &y& Elsevier]

A series of red-emitting phosphors of Sc 2 (MoO 4 ) 3 : x%Eu 3+ have been successfully synthesized at 800 °C by solid-state reaction. X-ray diffraction, scanning electron microscopy, photoluminescence spectra and decay curves were used to characterize the structures and luminescence properties. In the excitation spectrum, the strongest absorptions of 7 F 0 → 5 L 6 and 7 F 0 → 5 D 2 match well with the emission wavelength of the near-ultraviolet InGaN and blue GaN chips. The CIE value of Sc 2 (MoO 4 ) 3 : 40%Eu 3+ sample reaches (0.665, 0.334), which is very close to the NTSC standard (0.67, 0.33), demonstrating the highly pure red lights emitted. The decay curves of Eu 3+ : 5 D 0 → 7 F 2 emission exhibit a bi-exponential function excited by a 266 nm nanosecond-pulsed laser resulting from the lattice distortion which can speed up electric dipole transition. The good excitation profile and pure red emission indicate Sc 2 (MoO 4 ) 3 : Eu 3+ is a promising red-emitting phosphor for its application in commercial white light emitting diodes. [ABSTRACT FROM AUTHOR]

• By introducing Ce3+ into the CaLu 2 Mg 2 Si 3 O 12 (CLMSO):Cr3+, ultra-wide visible-NIR emission are realized. • The CLMSO:Cr3+, Ce3+ phosphor exhibit excellent thermal stability. • The electricity to Vis-NIR conversion efficiency can reached 30.5 %@10 mA and 29.5 % @10 mA for pc-LEDs fabricated with CLMSO:0.01Ce3+, 0.001Cr3+ and CLMSO:0.01Ce3+, 0.002Cr3+, respectively. In the past decade, the near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) and NIR phosphors has made considerable progress. However, for the field of non-destructive testing, ultra-wide Vis-NIR pc-LED light source can detect a wider range of components compared to NIR pc-LED. Therefore, the development of high-performance ultra-wide Vis-NIR phosphors is quite necessary. Based on the CaLu 2 Mg 2 Si 3 O 12 (CLMSO):Cr3+ with excellent performance, this article proposes the introduction of activator Ce3+ into CLMSO:Cr3+ phosphor, which significantly increase the emission band-width. Co-doped phosphor exhibit excellent thermal stability (maintain 75 % room temperature intensity @ 150 °C). The Vis-NIR light output power can reached 64.4 mW @ 100 mA and 60.9 mW@ 100 mA for pc-LED fabricated with CLMSO:0.01Ce3+, 0.001Cr3+ and CLMSO:0.01Ce3+, 0.002Cr3+ with the electricity to Vis-NIR conversion efficiency reached 30.5 %@10 mA and 29.5 % @10 mA, respectively. The CLMSO: Ce3+, Cr3+ phosphor is expected to become the new generation light sources for miniaturized spectrometer. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Ce3+ and Mn2+ co-doped Na 3 YSi 3 O 9 (NYS) phosphors with tunable emission were prepared via a high-temperature solid-state reaction. Under 320-nm excitation, Na 3 YSi 3 O 9 :Ce3+, Mn2+ exhibits two broad emission bands from 340 to 590 nm and from 525 to 700 nm, ascribed to the 5d-4f transition of Ce3+ and the 4T 1 (4G)-6A 1 (6S) spin-forbidden transition of Mn2+, respectively. Energy transfer from Ce3+ to Mn2+ through a dipole-dipole interaction was explained based on the luminescence spectra and fluorescence decay curves. The critical distance of energy transfer was calculated to be 12.836 Å, and the energy transfer efficiency reached as high as 91.9%. Temperature-dependent luminescence was studied, and the corresponding activation energy ∆ E was calculated to be 0.221 eV. Tunable luminescence from blue to orange was realized utilizing the energy transfer from Ce3+ to Mn2+. A warm white light with CIE chromaticity coordinates of (0.3627, 0.2855) and color temperature of 3612 K was achieved. These results indicate that NYS:Ce3+, Mn2+ may have potential application in UV-pumped white-light-emitting diodes. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

We demonstrate a blue emitting Ba 2 (Lu 0.98 La 0.02 ) 5 B 5 O 17 :Ce 3+ (BLLB:Ce 3+ ) phosphor prepared by high-temperature solid-state reaction. The pure phase of Ba 2 Lu 5 B 5 O 17 is difficult to obtain. To stabilize the crystal structure of Ba 2 Lu 5 B 5 O 17 , the larger ion radius of La 3+ was added to substitute Lu 3+ in raw materials. It is found that pure-phase Ba 2 Lu 5 B 5 O 17 is successfully obtained by adding 2% La 3+ . Upon 348 nm excitation, a luminescence internal quantum efficiency of BLLB:Ce 3+ can reach as high as 92%, which is comparable to the commercial blue phosphor BaMgAl 10 O 17 :Eu 2+ . The BLLB:Ce 3+ phosphor shows a blue emission band peaked at 443 nm with a main excitation band peaked at 348 nm. The dependence of luminescence intensity on Ce 3+ concentration was studied. The maximal luminescence intensity was observed at 1% Ce 3+ , which gives a critical distance of 2.41 nm between two Ce 3+ ions for luminescence quenching. The emission of the present phosphor is stable with increasing temperature up to its quenching temperature of 403 K. A white light emitting diode (WLED) was fabricated based on a near UV LED chip coated with a blend of the present blue phosphor, the commercial green (Ba,Sr) 2 SiO 4 :Eu 2+ and red CaAlSiN 3 :Eu 2+ phosphors. The WLED exhibited a low correlated color temperature of 4356 K with a high color rendering index of 93.2. These results suggest that BLLB:1% Ce 3+ can be utilized as a blue phosphor in UV based WLEDs. [ABSTRACT FROM AUTHOR]

In this paper, we synthesized series of Eu 2+ activated CaO ceramic powders by conventional solid state reaction. Using NH 4 Cl as a reducing additives, the Eu 3+ has been successfully reduced to Eu 2+ . An intense blue emission peaked at 460 nm from Eu 2+ was observed. The luminescent intensity of the doping-optimized CaO:Eu 2+ sample can be as high as 106% of commercial BAM blue phosphor under 400 nm near-ultraviolet (NUV) excitation. The effect of Eu 2+ and NH 4 Cl contents on photoluminescence properties and crystal phase formation have been investigated, respectively. The thermal stable property which is an important performance for LED application has also been measured. The emission intensity at 120 °C can maintain 94% of that at room temperature. Our results suggest that CaO: Eu 2+ ceramic powder could be used as a promising blue emitting phosphor for NUV chip based white LEDs. [ABSTRACT FROM AUTHOR]

• An efficient super broadband NIR phosphor is achieved by doping Nd3+ in Ca 2 LuZr 2 Al 3 O 12 : Cr3+. • The spectral range is extended and the IQE is improved due to efficient energy transfer from Cr3+ to the highly efficient Nd3+, in CLZA: Cr3+, Nd3+ phosphors. • Strong emission bands of Nd3+ with quantum efficiency close to 100% are observed, at around 900 nm and 1060 nm, which are complementary to Yb3+ emission, at 1030 nm. • An efficient super broadband NIR pc-LED with 350 nm bandwidth is achieved, in which the blend of CLZA: Cr3+, Nd3+and CLZA: Cr3+, Yb3+ phosphors are fluorescence converter. Near-infrared phosphor converted light emitting diodes (NIR pc-LEDs), as a compact light source, play a constructive role in wearable optical biosensing devices. In order to detect the properties of different substances, the NIR emission should be as wide as possible. The typical strategy for broadening the band is the superposition emission of Cr3+ and Yb3+, the bandwidth of which is 300–320 nm, and it needs to be further broadened. In this paper, NIR Ca 2 LuZr 2 Al 3 O 12 garnet phosphor, co-activated by Cr3+ and Nd3+, is prepared. The emission quantum efficiencies of Nd3+ at 900 nm and 1060 nm are close to 100%, and the emission band is complementary to that of Yb3+ at 1030 nm. An efficient super broadband NIR pc-LEDs (47.6 mW@100 mA), with the bandwidth of 350 nm, are achieved. The bandwidth and the efficiency of the pc-LEDs are improved greatly, compared with other reported ones. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we demonstrate a method to improve the photoluminescence of CaO: Ce3+ phosphor and delineate its first use in blue-pumped white LEDs. The results show that the yellow emission of Ce3+ is enhanced by a factor of 1.88 by adding Li+ into CaO host at 474nm blue light excitation. On analyzing the diffuse reflection spectra and fluorescence decay curves, we reveal that the photoluminescence enhancement is originated from the rise of absorbance to the excitation photons but not from the improvement of the luminescent efficiency. Li+-improved CaO: Ce3+ exhibits more red component when it is compared with the commercial Y3Al5O12: Ce3+ (YAG: Ce3+) phosphor, indicating its potential application for high color rendering white LEDs. Thus, a white LED is fabricated by combining blue InGaN LED chip with CaO: Ce3+, Li+ phosphor and a warm white light with high color rendering index (R a ) of 80, low correlated color temperature (T c ) of 4524K, and sufficient luminous efficiency of 50lmW−1 is obtained. [Copyright &y& Elsevier]

Abstract: Expanded emission spectra ranging from green to red are reported in Ca3Sc2Si3O12 (CSS):Ce3+,Mn2+ silicate garnets. Mn2+ may occupy Ca2+ site (Mn2+(I)) to generate a yellow emission band at 574nm or Sc3+ site (Mn2+(II)) with red emission band at 680nm. Efficient energy transfers from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) occur upon blue excitation into Ce3+. Concentration dependence of Mn2+ emission is analyzed based on Ce3+–Mn2+ energy transfer, steady state rate equations, and fluorescence lifetimes. Energy transfer efficiency (η T) and rate (W) are calculated with values as high as 45% and 14.01×106 s−1, respectively. [Copyright &y& Elsevier]

Abstract: Luminescence properties of the yellow-emitting (Ca2Lu1−x Ce x )(ScMg)Si3O12 (CLSM:xCe3+ x =0.01–0.15) phosphor are investigated for various Ce3+ concentrations. Different Ce3+ emission sites and energy transfers between them are observed, resulting in a red shift of the emission spectra from 530 to 575nm with increasing x from 0.01 to 0.15. Combining with blue (460nm) InGaN LEDs, CLSM:Ce3+ shows excellent performances for phosphor-converted white LEDs with higher color rendering index R a of 87.4–87.9 and lower color temperature T C of 5034–5814K, especially for warm pcWLEDs with a high color rendering (R a >80) and a low color temperature (T C <4000K). Thermal quenching behaviors depending on Ce3+ concentrations and temperatures are discussed. [Copyright &y& Elsevier]

Abstract: The yellow-emitting phosphor [Ca3−(x+0.06)Lu x Ce0.06](Sc2−y Mg y )Si3O12 obtained from Lu3+ and Mg2+ co-modified green-emitting silicate garnet Ca3Sc2Si3O12:Ce3+ (CSS:Ce3+) exhibits promising applications for white LEDs. In this paper, we discuss the effect of charge balance on the garnet structure formation. The changes of bond length and covalence caused by the replacement of Lu3+ and Mg2+ for Ca2+ and Sc3+ are analyzed. The shift of the Ce3+ emission and excitation can be attributed to the combined results from crystal field splitting effect and centroid shift of Ce3+ 5d levels. Thermal stability is analyzed according to configurational coordinate diagram. [Copyright &y& Elsevier]

Abstract: Green-emitting phosphor Ca8Zn(SiO4)4Cl2:Eu2+ has been prepared by the solid state reaction method and there luminescence properties are investigated. The excitation spectrum of Ca8Zn(SiO4)4Cl2:Eu2+ shows an intense excitation band in the blue centered at 450nm and emits with a maximum at 505nm. The concentration quenching mechanism is studied and verified to be the energy transfer among the nearest-neighbor ions. Upon 450nm excitation, the emission intensity of Ca8Zn(SiO4)4Cl2:Eu2+ is much stronger than the green emitting Ca3SO4Cl2:Eu2+ phosphor and even higher than YAG:Ce3+. This excitation spectrum range matches UV and blue light-emitting diodes (LEDS) chips very well, suggesting Ca8Zn(SiO4)4Cl2:Eu2+ could be a promising green emitting phosphor candidate for LED devices. [Copyright &y& Elsevier]

Abstract: 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 505nm of Eu2+ and a yellow band at 550nm of Mn2+. The excitation spectra corresponding to 4f7-4f65d transition of Eu2+ cover the spectral range of 370–470nm, 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. [Copyright &y& Elsevier]

Abstract: A series of Eu2+ and Mn2+ coactivated Ca3Al2(SiO4)3− δ Cl4 δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca3Al2(SiO4)3− δ Cl4 δ :Eu2+, Mn2+ exhibits two dominating bands situated at 460 and 550nm, originate from the allowed 5d → 4f transition of the Eu2+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the decline of lifetimes of Eu2+. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca3Al2(SiO4)3− δ Cl4 δ :Eu2+, Mn2+ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes. [Copyright &y& Elsevier]

Abstract: Ce3+ and Mn2+ co-doped Ca4Si2O7F2 phosphors have been synthesized by high temperature solid state reaction and their luminescence properties are investigated. The effect of Ce3+ concentration on the emission intensity of Ca4Si2O7F2: Ce3+ is studied, and the emission intensity reaches a maximum at 4% Ce3+. Energy transfer from Ce3+ to Mn2+ is observed. The emission spectra of the phosphors show a blue broad band at 460nm of Ce3+ and a yellow band at 580nm of Mn2+, originate from the allowed 5d→4f transition of the Ce3+ ion and the 4T1g(4G)→ 6A1g(6S) transition of the Mn2+ ion, respectively. Results indicate that the varied emitted color from blue to yellow can be achieved by tuning the relative ratio of the Ce3+ to Mn2+ ions based on the principle of energy transfer. We have demonstrated that Ca4Si2O7F2: Ce3+, Mn2+ phosphors can be a promising candidate for a color-tunable phosphor applied in a near-UV White light emitting diodes. [Copyright &y& Elsevier]

Abstract: A yellow-emitting phosphor, CaO:Ce3+,Na+ is synthesized by solid-state reaction. The photoluminescence spectra, fluorescence decay curves and the temperature-dependent luminescence are investigated. The results show that CaO:Ce3+,Na+ can be excited by blue light, which matched well with the emission wavelengths of blue InGaN LED chips. When excited at 474nm, in the range of 480–700nm, CaO:Ce3+,Na+ exhibits a strong yellow emission band located around 555nm. The temperature-dependent luminescence behavior of this phosphor indicates that CaO:Ce3+,Na+ exhibits better thermal stability than commercial YAG:Ce3+. [Copyright &y& Elsevier]

K2Al2B2O7:Eu2+ phosphor is prepared by reaction of a stoichiometric HNO3 solution of Eu2O3, K2CO3, Al(NO3)3, and H3BO3 followed by drying and sintering in a reducing CO atmosphere (C sticks covered crucible, 1. [ABSTRACT FROM AUTHOR]