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Red and far‐red spectral components are the basics for color rendering improvement of illumination devices and growth regulation of plants, respectively. Establishing a feasible design principle in solid state materials for the red/far‐red phosphors is significant but challenging. Realizing metal to metal charge transfer (MMCT) in Bi3+‐doped phosphors is a new strategy to target the red/far‐red luminescence. As a proof of concept, the MMCT state involving the ground state of Bi3+ ion and the excited state of host (Nb/Ta)5+ cations in Na2Ca3(Nb, Ta)2O9:Bi3+ induces efficient and tunable yellow/far‐red luminescence (peaking at 597–667 nm). Moreover, benefited from the appropriate distance between Bi3+ and (Nb/Ta)5+ ions, Na2Ca3(Nb, Ta)2O9:Bi3+ possess intense absorption in near‐ultraviolet region and no absorption in visible region. The plant growth light with the blending of Na2Ca3Nb2O9:Bi3+ far‐red phosphor and BAM:Eu2+ blue phosphor yields broadband electroluminescence covering almost the entire absorption spectra of chlorophyll and phytochrome, which is superior to the Cr3+‐ and Mn4+‐based light‐emitting diode (LED) devices. The white‐LED device by employing Na2Ca3Ta2O9:Bi3+ yellow phosphor as the essential component yields full‐spectrum warm white light with high color indexes. [ABSTRACT FROM AUTHOR]

Ce 3+ , Tb 3+ co-doped T-phase orthosilicate Ba 1.2 Ca 0.8 SiO 4 phosphors were prepared by means of solid state reactions. The synthesized samples were investigated using XRD and PL emission and excitation spectra. The emission spectra for Ce 3+ doped Ba 1.2 Ca 0.8 SiO 4 phosphors show broad bands in the 320–550 nm spectral region. The excitation spectra exhibit several absorption peaks in the range of 250–400 nm. Both the emission and excitation spectra are dependent on the excitation or monitoring wavelengths. We attribute these results to Ce 3+ ions occupying two different crystallographic sites (i.e., Ce I and Ce II). The Ce 3+ , Tb 3+ co-doped Ba 1.2 Ca 0.8 SiO 4 phosphors show Tb 3+ -related line emissions in the 475–600 nm spectral region and Ce 3+ -related band emissions in the 350–525 nm spectral region when the 4 f → 5d transition of Ce 3+ is excited (λ ex  = 345 nm), indicating that energy transfer from Ce 3+ to Tb 3+ takes place. Moreover, the emission intensity of 5 D 4 → 7 F 5 transition for Ba 1.00 Ce 0.02 Tb 0.08 Li 0.10 Ca 0.8 SiO 4 is 30 times stronger than that of Ba 1.04 Tb 0.08 Li 0.08 Ca 0.8 SiO 4 sample under 345-nm UV excitation. [ABSTRACT FROM AUTHOR]

A series of K 2 MgSi 3 O 8 : x Ce 3+ ( x = 0.01–0.09), K 2 MgSi 3 O 8 :0.05Ce 3+ , y Tb 3+ ( y = 0–0.09) phosphors was prepared by solid-state method. X-ray diffraction was used to determine the crystal phase. Luminescence properties were characterized by photoluminescence (PL), photoluminescence excitation (PLE) spectra at room temperature. K 2 MgSi 3 O 8 : x Ce 3+ series emits blue light when excited by UV-light (λ ex = 350 nm). Nonequivalent substitution of K + for Ce 3+ leads to the multiple Ce 3+ centers in the compound. K 2 MgSi 3 O 8 :Ce 3+ , Tb 3+ exhibits broad band emission of Ce 3+ and the characteristic line emission of Tb 3+ . The luminescence color could be tuned from blue (0.16, 0.10) to greenish blue (0.19, 0.26) by varying Tb 3+ content. The energy transfer has been confirmed to occur via quadrupole-quadrupole interaction. These results indicate that the K 2 MgSi 3 O 8 :Ce 3+ , Tb 3+ phosphor might be a promising material for w-LEDs application. [ABSTRACT FROM AUTHOR]

The Eu 2+ , Ce 3+ , Tb 3+ and Ce 3+ -Tb 3+ doped ternary metal diphosphate K 2 Ba 3 (P 2 O 7 ) 2 is prepared using high temperature solid state synthesis. K 2 Ba 3 (P 2 O 7 ) 2 :Eu 2+ shows a deep blue emission ( λ max = 405 nm) when it is excited by UV lights. The broad peak at 405 nm can be decomposed to two Gaussian curves with maxima at 405 and 440 nm which can be attributed to the presence of two crystallographically different Eu 2+ sites in the crystal structure. The emission spectrum of K 2 Ba 3 (P 2 O 7 ) 2 :Ce 3+ is dependent of the excitation wavelength that also results from the two crystallographically different Ce 3+ sites. The emission spectrum of K 2 Ba 3 (P 2 O 7 ) 2 :Tb 3+ shows the 5 D 3 and 5 D 4 emission lines. The f-d spin-allowed and spin-forbidden transitions in Tb 3+ in K 2 Ba 3 (P 2 O 7 ) 2 are at about 225 and 250 nm, respectively. For the (Ce 3+ , Tb 3+ ) co-doped K 2 Ba 3 (P 2 O 7 ) 2 system, the energy transfer from Ce 3+ to Tb 3+ is observed. [ABSTRACT FROM AUTHOR]

The unusual photoluminescence (PL) properties and temperature dependent decay behavior of Eu 2+ in KBaBP 2 O 8 are reported and discussed. The emission spectrum is so complicate that it can be deconvoluted into three fitting peaks. The emission bands peaking at 380 and 444 nm can be assigned to the 4f 6 5d 1 →4f 7 transition of Eu 2+ centers substituting for K + and Ba 2+ site, while the emission band at 497 nm may be attributed to the Eu 2+ center on K + site with a nearby charge-compensated vacancy. The decay time of the 4f 6 5d emission increases with temperature. This increase can be explained by either thermal population of the 4f 7 ( 6 P 7/2 ) level or thermal population of higher energetic 4f 6 5d states. [ABSTRACT FROM AUTHOR]

The luminescence properties of Eu 2+ in AgCa 10 (PO 4 ) 7 has been studied at room and low temperature and the decay times of Eu 2+ in this matrix have been measured and analyzed. According to the crystal structure of AgCa 10 (PO 4 ) 7 , photoluminescence (PL) spectra and decay curves, the substitution of Eu 2+ ions is possible to four different Ca 2+ sites. The red-shift of emission wavelength and energy transfer process between Eu 2+ activator ions are discussed. [ABSTRACT FROM AUTHOR]

The optical properties of LiBaBO3 doped with Eu2+ are investigated in the temperature regime between 10 and 525 K for the first time. At room temperature (RT), a broad emission band peaking around 485 nm is observed. The emission is ascribed to the 4f65d1 → 4f7 transition on Eu2+. The excitation spectra consist of broad bands between 220 and 450 nm. The emission intensity shows no remarkable decline at lower temperatures; although it decreases drastically at higher temperatures. The Stokes shift is calculated to be 0.52 eV. The thermal activation of an electron from the Eu2+ excited state to the conduction band is responsible for the thermal quenching behavior in LiBaBO3:Eu system. The energy gap EA for the best fit of decay time is 0.38 eV. [ABSTRACT FROM AUTHOR]

This article reports on the optical properties of Sm3+-activated GdB3O6phosphors based on the measurement of their photoluminescence spectra and luminescence decay curves. Energy transfer from Gd3+to Sm3+and the concentration quenching of the Sm3+ion emission are investigated. From the photoluminescence spectra and decay curves, the energy transfer from Gd3+to Sm3+is confirmed. The concentration quenching of the Sm3+ion emission can be ascribed to resonant cross-relaxation. The interaction between the Sm3+ions is derived of the electric dipole–dipole type through fitting the data with the Inokuti-Hirayama model. The critical distances and energy transfer microparameter for the transfer processes are given. The decay curves of Sm3+4G5/2level exhibiting a buildup and decay process also confirm the energy transfer from Gd3+to Sm3+and between Sm3+ions. [ABSTRACT FROM PUBLISHER]

Highlights: [•] SrLiB9O15:Ce3+/Tb3+ phosphors were studied for the first time. [•] Ce3+ ions occupy two different sites (Ce I and Ce II) in SrLiB9O15 crystal. [•] Ce3+ ions substitute Sr2+ sites and interstitial sites simultaneously. [•] Energy transfer behavior from Ce3+ to Tb3+ is confirmed. [•] The energy transfer occurs from Ce II to Tb3+ in this case. [ABSTRACT FROM AUTHOR]

Abstract: Sn2+- and Sn2+/Mn2+-doped α-Sr2P2O7 phosphors have been synthesized by using the traditional solid-state reaction. The photoluminescence of Sn2+ and Sn2+/Mn2+ in α-Sr2P2O7 are reported and discussed. The Sn2+-activated material exhibits a blue-emitting band peaking at about 450nm under UV excitation. The Mn2+ emission peaking at about 565nm of Sn2+/Mn2+ co-doped samples can be enhanced through energy transfer from Sn2+ to Mn2+. Combining emission colors of Sn2+ and Mn2+ under UV excitation, white light emission can be achieved. [Copyright &y& Elsevier]

Abstract: 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 614.5nm due to electric–dipole transition. The excitation spectrum shows several sets of lines in the range of 350–425nm 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. [Copyright &y& Elsevier]

Highlights: [•] Lifetime of Gd decreases with Dy concentration, confirming energy transfer. [•] Rise time confirms the feeding of the Dy excited state by energy transfer. [•] Concentration quenching of Dy emission is ascribed to resonant cross-relaxation. [•] Interaction between Dy ions is dipole-dipole type through fitting with I-H model. [ABSTRACT FROM AUTHOR]

Scheelite-type Eu3+-activated molybdates [(Sr1−2 xEu xLi x)MoO4 and Sr0.40Eu0.40MoO4)] were prepared by the high temperature solid state reaction. The phase purity of the phosphors was characterized by XRD. The PL spectra, the fluorescence decay curves and the dependence of luminescence intensity on temperature were investigated in detail. The phosphors can be efficiently excited by near-UV light to realize an intense red luminescence corresponding to the electric dipole transition of Eu3+ ions. The external quantum efficiency of (Sr0.2Eu0.4Li0.4)MoO4 sample under 395-nm excitation is 0.73. According to the PL spectra, these phosphors could be candidate red-emitting materials for solid-state lighting if they are combined with green and blue efficiency phosphors and suitable near-UV InGaN chip. [ABSTRACT FROM AUTHOR]

Abstract: A novel Li5La3Nb2O12:Eu3+ phosphor was synthesized by the solid-state reaction at high temperature. The phase purity of products was checked by XRD. The emission spectrum is independent of the excitation wavelength and the 5D0–7F2 transition is the dominant one. In the excitation spectrum, there are some sharp peaks originating from the f–f transitions of Eu3+ and a broad band peaking at about 280nm. The concentration dependence of emission intensity and decay curves of 5D0–7F2 transition were investigated. The temperature dependence of emission intensity and decay curves were also investigated in detail. [Copyright &y& Elsevier]

Abstract: Tb3+ ions activated Li4SrCa(SiO4)2 phosphors were synthesized using a solid state reaction method. The phase impurity was checked by XRD. The photoluminescence (PL) excitation spectrum, emission spectra at room and high temperature, decay curves of samples with different Tb3+ ions concentration were studied in detail. Cross-relaxation and the Inokuti–Hirayama model were used to analyze the experimental results. Li4SrCa(SiO4)2:xTb3+ are thermally stable and color tunable phosphors. [Copyright &y& Elsevier]

Abstract: (Gd1−x Eu x )(BO2)3 (0≤x≤1) phosphors are synthesized by traditional high temperature solid state reaction. The photoluminescence (PL) properties of Gd(BO2)3 and Gd(BO2)3 activated with Eu3+ are investigated. The PL spectra exhibit the typical characteristic emission and excitation of Gd3+ and Eu3+ ions, and support the energy transfer taking place from Gd3+ to Eu3+ ions. The relationship between Eu3+ doping concentration and emission intensity is also studied. Even if all of the Gd3+ ions are substituted by Eu3+ ions, the concentration quenching between Eu3+ happens. However, the quenching is not complete. The luminescence decay curves are measured, and the lifetimes become short with the Eu3+ content increasing. The decreasing Gd3+ lifetimes also indicates that there exists efficient energy transfer between Gd3+ and Eu3+ ions. [Copyright &y& Elsevier]

Abstract: Sr2Mg(BO3)2:Ce3+,Li+ and Sr2Mg(BO3)2:Ce3+,Li+,Mn2+ phosphors have been synthesized by conventional solid state reaction technology at 900°C for 12h in reducing atmosphere. The phase purity, photoluminescence (PL) properties, thermal stability, energy transfer and luminescent decay curves have been investigated. Sr2Mg(BO3)2:Ce3+,Li+,Mn2+ phosphors show blue and deep-red [1] For interpretation of color in Figs. 1–6, the reader is referred to the web version of this article. 1 emission bands. The deep-red emission band is attributed to the energy transfer from Ce3+ to Mn2+. The fluorescence lifetimes of Ce3+ in co-doped sample are shorter than that in single doped one, which confirms that the energy transfer takes place. The phosphors have weak thermal quenching. The luminescence properties of Sr2Mg(BO3)2:Ce3+,Li+,Mn2+ make the phosphor a new bicolor emitting material. [Copyright &y& Elsevier]

Abstract: Sr2LiSiO4F co-doped with Ce3+, Mn2+ have been synthesized by means of solid state reactions. Their photoluminescence (PL) emission spectra, excitation spectra and the decay profiles of Ce3+ emission have been measured at room temperature. The emission peak around 410nm is ascribed to the 5d1 to 2F5/2 and 2F7/2 transitions of Ce3+ ions, while the peak around 680nm is ascribed to the 4T1–6A1 transition of Mn2+ ions. The decay rate of the 5d state within Ce3+ ion under 355nm laser excitation becomes faster with the increase of Mn2+ concentration. The analysis of the observed spectra confirms that there exists energy transfer from Ce3+ to Mn2+. [Copyright &y& Elsevier]

Abstract: Orange-emissive Ce3+/Eu2+ co-doped Sr3Al2O5Cl2 phosphors were synthesized by a solid-state reaction. The large overlap between the emission spectrum of blue Sr3Al2O5Cl2:Ce3+ and the excitation spectrum of orange Sr3Al2O5Cl2:Eu2+, and the shortening trend in lifetime of Ce3+ donors with increasing Eu2+ concentration in Sr3Al2O5Cl2:Ce3+, Eu2+ provide the strong evidence of energy transfer from Ce3+ to Eu2+ ions. It supports that the orange emission intensity of the optimal co-doped phosphor is 1.5 times stronger than that of single Eu2+-doped one. The Sr3Al2O5Cl2:Ce3+, Eu2+ phosphor is a promising orange-emitting phosphor for warm-white-light-emitting diode because of its effective excitation in the near ultraviolet range. [Copyright &y& Elsevier]

The luminescence properties and site occupation of NaScP 2 O 7 :Ce 3+ and KScP 2 O 7 :Ce 3+ phosphors are reported for the first time. Two principal Ce 3+ sites [Ce (I) and Ce (II)] are observed. One of the Ce 3+ centers is found to be produced by the direct substitution of the dopant ion for Na + /K + without a local charge compensation. Another center is ascribed to an associate of a Ce 3+ ion and a cation vacancy. The zero-phonon line E 0 and Stokes shift are calculated. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Mn2+-doped Ba2ZnS3 phosphors for white light emitting diodes (LEDs) have been prepared by high temperature solid-state reaction and their photoluminescence properties are reported. Diffuse reflection spectra of Ba2ZnS3 host and synthesized phosphors have been measured. The excitation spectrum extends a broad range of wavelength and is consistent with the diffuse reflectance spectra. The emission bands are due to 4T1(4G)→ 6A1(6S) transition of the Mn2+ ion and there exists efficient energy transfer from host to Mn2+ ions. The dependence of emission wavelength on Mn2+ concentration is studied. The decay curve of Mn2+ ions luminescence in Ba2Zn0.995S3:0.005 Mn2+ is also measured. [Copyright &y& Elsevier]

Abstract: The synthesis and photoluminescence properties of novel Eu2+ doped Ba2ZnS3 phosphors for white light emitting diodes (LEDs) are reported. Diffuse reflection spectra of Ba2ZnS3 host and synthesized phosphors have been measured. The excitation spectra of synthesized phosphors consist of three broad bands between 250 nm and 550 nm and are consistent with the diffuse reflectance spectra. The emission spectra show the characteristic 4f65d1 →4f7 transition of Eu2+ ion and there exists efficient energy transfer from host to Eu2+ ions when excited by 350-nm light. The dependence of emission spectra on temperature is also measured; the possible reasons applied to explain the experimental results are also discussed. The fluorescence lifetime of Eu2+ in Ba1.995ZnS3:0.005Eu2+ is measured and the values are 1.49 and 23.4 μs. [Copyright &y& Elsevier]

Abstract: Infrared to visible up-conversion emissions in Yb3+–Er3+ co-doped KGd2F7 samples excited at 980 nm are presented in this paper. Green (2H11/2,4S3/2→4I15/2), red (4F9/2→4I15/2) and violet (2H9/2→4I15/2) emissions are observed under low pumping power, and the green emission is dominant. The dependences of these emissions as function of the pumping power intensities and the doped rare-earth ion concentrations are described. The results indicate that the green and red emission of Er3+ ion result from two-photon excitation processes, and the violet emission of Er3+ ion from three-photon processes. The most efficient composition for green emission is 2–4 mol% Er3+ and 10–20 mol% Yb3+ in synthesized samples. The mechanisms for explaining these up-conversion properties have been provided. [Copyright &y& Elsevier]

Abstract: Novel phosphors of Eu2+-doped (Ca1−xSrx)Se for the application of white light emitting diodes (LEDs) were prepared by conventional solid-state reaction. Diffuse reflection spectra of CaSe, SrSe, CaSe:Eu2+ and SrSe:Eu2+ were measured. The excitation spectra consisted of two broad bands and were consistent with the diffuse reflectance spectra. The emission band is due to the 4f65d1→4f7 transition of the Eu2+ ion. With an increase in x, the emission band shifted to shorter wavelength and the reason was discussed. The fluorescence lifetimes of Eu2+ in (Ca1−xSrx)Se:0.04Eu2+ were also measured and the values were reasonable for the allowed transition 4f65d1→4f7 in Eu2+. [Copyright &y& Elsevier]

Abstract: Novel phosphor of Eu2+-doped SrLaGa3S6O was prepared by solid-state reactions at 900°C and H2S atmosphere. The excitation and emission spectra of this phosphor showed that all were broadband due to 4f7–4f65d1 transitions of Eu2+. The phosphors with different Eu2+ concentrations presented yellowish-green luminescence for both UV and visible excitation (200–500nm). The concentration quenching mechanism was verified as quadrupole–quadrupole interaction and the value of the critical transfer distance was calculated as 17Å. The fluorescence lifetime of Eu2+ was also measured. [Copyright &y& Elsevier]

Abstract: Eu3+- and Tb3+-activated SrGdGa3O7 phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd1− x Eu x )Ga3O7 and Sr(Gd1− x Tb x )Ga3O7 formed continuous solid solution in the range of x =0–1.0. Unactivated SrGdGa3O7 exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa3O7:xEu3+ and SrGdGa3O7:xTb3+ phosphors also showed the well-known Eu3+ and Tb3+ excitation and emission. The energy transfer from Gd3+ to Eu3+ and Tb3+ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu3+ and Tb3+ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa3O7:Eu and SrGdGa3O7:Tb were compared with commercial phosphors, Y2O3:Eu and LaPO4:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu3+ and Tb3+ were in the range of microsecond. The energy transfer from Gd3+ to Tb3+ was also observed in decay curve. [Copyright &y& Elsevier]

Color-tunable luminescence in phosphors can be achieved in a number of ways. In this study, a series of Ce3+/Tb3+ singly doped and (Ce3+,Tb3+) doubly doped Sr 5 (BO 3) 3 F (SBOF) phosphors, having color point tuning properties, were synthesized by solid-state reaction. The emission color can be adjustable in two ways: by means of changing Ce3+ concentration or doubly doping Ce3+ and Tb3+ ions. The variation in the Ce3+ concentration in Ce3+ singly doped SBOF shows a red shift of the emission. The red shift can be assigned to energy transfer between Ce3+ ions at different sites. In the SBOF:Ce3+,Tb3+ samples, adjustable emission from blue to green can also be obtained by changing Tb3+ doping concentration when Ce3+ content is fixed under UV excitation. This is due to the energy transfer process from Ce3+ to Tb3+ in SBOF:Ce3+,Tb3+ phosphors. Moreover, the characteristic emission peak intensity of Tb3+ in the co-doped sample is enhanced by about 40 times compared with the single-doped Tb3+ phosphor under near-ultraviolet excitation. The potential application of this green-emitting phosphor in UV chip excited white LED was evaluated. [ABSTRACT FROM AUTHOR]

Abstract: A novel blue-emitting Sr3Al2O5Cl2:Ce3+,Li+ phosphor has been synthesized by solid state reaction. The excitation spectrum shows a broad band extending from 300 to 400 nm, and the emission spectrum shows a broad blue band peaking at 450 nm with a half width of about 100 nm. The emission intensity at 250 °C remains at about 50% of that at room temperature. The decay curve at the emission peak consists of fast and slow components. The Sr3Al2O5Cl2:Ce3+,Li+ should be a promising blue phosphor for near ultraviolet-based white-light-emitting diodes. [Copyright &y& Elsevier]

Abstract: (Ca1+ x − y Eu y )Ga2S4+ x phosphors have been synthesized one step by solid state reaction. The photoluminescence excitation and emission spectra of phosphors have been studied; the influence of host composition and Eu2+ concentration on emission spectra has also been investigated. The emission spectrum consists of yellow emission at 550 nm and red emission at 650 nm. It also indicates that the excitation spectrum is a broadband and can be well matched with the emission of GaN chip. Combined these phosphors with 460 nm-emitting GaN chips, White LEDs have been fabricated. Their electroluminescence spectra have been measured under 20 mA forward-bias current. Their CIE chromaticity coordinates and color temperature indicate that (Ca1+ x − y Eu y )Ga2S4+ x phosphors are promising phosphors for GaN-based white LEDs. [Copyright &y& Elsevier]

Charge compensating defects, resulting from heterovalent cation substitution, often play an important role in luminescent properties. In this paper, the luminescence properties of K 2 MgSi 3 O 8 :Eu2+ phosphor were studied by means of XRD, PL and decay analysis. It is found that there was only one K+ site to be substituted by Eu2+ in the K 2 MgSi 3 O 8 host lattice. However, the existence of multiple Eu2+ sites is observed, which is explained by charge compensating mechanism. Unequal substitution is a meaningful way to discover new luminescent materials. [ABSTRACT FROM AUTHOR]

Abstract: Novel Eu3+-doped NaCa4(BO3)3 phosphors were synthesized by solid-state reactions. The emission spectra exhibit well-known transitions from the 5D0 level to the lower 7F manifold. The excitation spectrum monitored with 613nm consists of broad excitation band peaking at 265nm and some narrow lines originated from the typical Eu3+ intra-4f6 transitions. The optimum Eu3+ doped concentration, the critical distance of the concentration quenching, the fluorescence decay curves, and the mechanism of concentration quenching are investigated. [Copyright &y& Elsevier]

Red light in sunlight promotes plant growth and development, while UV and green light are poorly absorbed by plants. Converting UV and green light into red light can enhance solar energy utilization and improve photosynthetic efficiency, significantly shortening the plant growth cycle. Herein, we report a novel red-emitting Sr 2 In 0.5 Sb 0.5 O 4 :Mn4+ phosphor that can be effectively excited by both UV and green light. According to Dexter's theory, Mn4+ is calculated to be in a weak crystal field. When excited at 330 or 520 nm, the characteristic photoluminescence (PL) peak appears at ∼695 nm, which is attributed 4T 2g → 4A 2g transition of Mn4+. The optimal doping concentration of Mn4+ is 0.003, and the concentration quenching mechanism was determined to be a dipole-dipole interaction. Additionally, a red LED device was fabricated by encapsulating Sr 2 In 0.5 Sb 0.497 O 4 :0.003Mn4+ phosphor with a 365 nm UV chip, exhibiting bright red light when driven by 150 mA current. The corresponding electroluminescence (EL) spectrum matches well with the absorption spectra of phytochromes P R and P FR , indicating that Sr 2 In 0.5 Sb 0.5 O 4 :Mn4+ phosphor has promising applications in plant growth. • We developed a novel red-emitting Sr 2 In 0.5 Sb 0.5 O 4 :Mn4+ phosphor that can be excited by both UV and green light. • Its emission spectrum matches well with the absorption spectra of phytochromes P R and P FR. • It can convert the UV and green light into red light that can be absorbed by plants, enhancing solar energy utilization. [ABSTRACT FROM AUTHOR]

Abstract: A novel blue-emitting Sr3Ga2O5Cl2:Eu2+ phosphor has been synthesized by a two-step solid-state reaction. The luminescence properties have been investigated by photoluminescence (PL) spectra, and temperature-dependent PL spectra. It shows an efficient broad absorption band around 400nm, which matches well with the commercial near-ultraviolet light-emitting chips, and an efficient blue emission. It shows a higher thermal quenching temperature than that of Sr3Al2O5Cl2:Eu2+ phosphor. Sr3Ga2O5Cl2:Eu2+ phosphor is a promising blue-emitting component for UV chip excited white light-emitting-diodes. [Copyright &y& Elsevier]

A detailed investigation on photoluminescence properties and energy transfer mechanism of Tb3+/Mn2+ singly doped and co-doped T-phase orthosilicate Ba 1.2 Ca 0.8 SiO 4 (BCS) phosphors, synthesized by conventional solid state reaction, is provided. All the samples were investigated by X-ray diffraction (XRD), photoluminescence spectroscopy and fluorescence decay curve. The Mn2+ emission intensity of BCS:Tb3+, Mn2+ is 28 times stronger than that of BCS:Mn2+. In addition, the emission color of BCS:Tb3+, Mn2+ phosphors can be tuned from green to orange-red by varying Mn2+ concentration. The efficient energy transfer from Tb3+ to Mn2+ is responsible for these phenomena. By employing the Inokuti–Hirayama model and Dexter's energy transfer theory, the dipole–dipole interaction is confirmed as the predominant multipolar effect in controlling this energy transfer process. • Tb3+/Mn2+ doped T-phase orthosilicate Ba 1.2 Ca 0.8 SiO 4 phosphors were synthesized. • Emission intensity of Mn2+ for BCS:Tb3+,Mn2+ is enhanced than that of BCS:Mn2+. • Energy transfer mechanism is confirmed based on I–H model and Dexter's theory. • Emission color of BCS:Tb3+,Mn2+ can be tuned from green to red-orange. [ABSTRACT FROM AUTHOR]

Y 4 Zn 4 (SiO 4) 5 silicate doped with Eu3+ ions was prepared by the high temperature solid state method. The phase purity of phosphor series (Y 4- x Eu x)Zn 4 (SiO 4) 5 (0.004 ≤ x ≤ 4) was checked by X-ray diffraction. The crystal structure, interatomic distances, and atom coordination numbers of Eu 4 Zn 4 (SiO 4) 5 were determined using x-ray powder diffraction. A study of the luminescent properties of (Y 4- x Eu x)Zn 4 (SiO 4) 5 was carried out employing photoluminescence excitation and emission spectra and luminescence decay. The occupied sites of Eu3+ ions, relative intensity between magnetic dipole transition and electric dipole transition and the 7F J levels splitting by the crystal field were discussed in terms of a low symmetry site of Y3+ ion in the Y 4 Zn 4 (SiO 4) 5 host lattice. The concentration quenching of Eu3+ luminescence was also investigated from the concentration dependence of the decay time measured for Eu3+5D 0 → 7F 1,2 luminescence. • Compounds Eu 4 Zn 4 (SiO 4) 5 and Y 4 Zn 4 (SiO 4) 5 were isostructural. • Only one Eu3+ site was confirmed based on emission line of 5D 0.→ 7F 0 transition. • 5D 0.→ 7F J transitions split into multiple peaks were due to low symmetry Eu site. • The interaction mechanism between Eu3+ ions was the dipole-dipole coupling. [ABSTRACT FROM AUTHOR]

Ce3+, Tb3+ and Ce3+-Tb3+ activated Ba 3 Y 2 (B 2 O 5) 3 phosphors were synthesized by a sol-gel pyrolysis method. The synthesized phosphors were investigated using X-ray diffraction (XRD) analysis, photoluminescence emission and excitation spectra and luminescence decay curves. In the Ce3+ activated Ba 3 Y 2 (B 2 O 5) 3 samples, two different Ce3+ centers (marked as Ce(1) and Ce(2)) could exist. The Ba 3 Y 2 (B 2 O 5) 3 :Tb3+ phosphor shows some emission peaks at ∼350–650 nm among which the green emission peak at 540 nm is the strongest. For the Ba 3 Y 2 (B 2 O 5) 3 :Ce3+, Tb3+ co-doped phosphor, the existence of energy transfer process from Ce3+ center to Tb3+ center is confirmed and the interaction mechanism between Ce3+ and Tb3+ in Ba 3 Y 2 (B 2 O 5) 3 :Ce3+,Tb3+ system is dipole-dipole interaction based on Inokuti–Hirayama (I H) model. • PL properties of Ce3+, Tb3+ and (Ce3+-Tb3+) activated Ba 3 Y 2 (B 2 O 5) 3 were studied. • Ce3+ site occupancy is investigated. • Two different Ce3+ centers (Ce1 and Ce2) exist in Ba 3 Y 2 (B 2 O 5) 3 host lattice. • The energy transfer from Ce3+ center to Tb3+ center takes place. [ABSTRACT FROM AUTHOR]

Abstract Photoluminescence properties of CaS:Cu+, CaS:Mn2+ and CaS:Cu+, Mn2+ rare-earth -free phosphors prepared by a carbon-thermal reduction method were investigated. The emission spectrum of Cu+-doped CaS consists of two overlapped bands peaking at 415 nm (attributed to isolated Cu+ activator) and 475 nm (attributed to aggregated Cu+ center). The influence of Cu+ doping concentration on the emission spectrum is discussed. The emission spectrum of Mn2+-doped CaS exhibits a band emission peaking at 568 nm under 250 nm excitation. The emission spectra of the doubly activated CaS:Cu+, Mn2+ phosphors consist of Cu+ and Mn2+ emissions simultaneously, and their shapes depend strongly on the Mn2+ concentration. Based on the emission and excitation spectra of the CaS:0.15 mol%Cu+, x Mn2+ phosphors, the energy transfer from Cu+ to Mn2+ takes place. The emitting colors of the doubly activated phosphors can also be tuned. In particular, the emitting color of CaS:0.15 mol% Cu+, 0.6 mol % Mn2+ sample is close to white light. Highlights • The phosphors are rare-earth free. • The phosphors are prepared by a simple carbon-thermal reduction method. • The energy transfer from Cu+ to Mn2+ takes place. • The emitting colors of the phosphors can be turned. • CaS:Cu+, Mn2+ could be a phosphor emitting white light in a single host. [ABSTRACT FROM AUTHOR]

The temperature dependence of photoluminescence properties and decay times in the range 10–300 K is reported for Eu 2+ doped NASICON-type phosphate CaZr 4 (PO 4 ) 6 . Luminescence from the Eu 2+ impurity has been investigated. Two different Eu 2+ centers have been detected in the host structure, 3a and 3b, corresponding to the emission bands peaking at 531 and 480 nm. The emission intensity and lifetimes decrease with increasing temperature due to temperature quenching. The values of Stokes shift, quenching temperature T 1/2 and activation energy for thermal quenching are evaluated. The mechanism of thermal quenching is also discussed. [ABSTRACT FROM AUTHOR]

New potassium gadolinium phosphate [K 3 Gd 5 (PO 4 ) 6 ] doped with Eu 3+ , Ce 3+ , Tb 3+ and co-doped with Ce 3+ and Tb 3+ phosphors were prepared by high temperature solid state synthesis. Phase purity of the powders was checked by X-ray powder diffraction. Luminescence and excitation spectra of samples were reported. In particular, the interaction mechanism between Eu 3+ ions was investigated in terms of the Inokuti–Hirayama model; it was found that the interactions between Eu 3+ can be assigned to dipole–dipole interaction. K 3 Gd 5 (PO 4 ) 6 :Eu 3+ could act as a candidate for solid state lighting due to its strong absorption band in the near-UV region (350–400 nm). The energy transfer from Ce 3+ to Tb 3+ was confirmed and the mechanism was studied using Dexter's theory; it is concluded that electric dipole–dipole interaction predominates in the energy transfer process from Ce 3+ to Tb 3+ in the K 3 Gd 5 (PO 4 ) 6 host. The energy transfer efficiency and critical distance were also investigated. [ABSTRACT FROM AUTHOR]

Compared with traditional incandescent and fluorescent lamps, phosphor-converted white light-emitting diodes (LEDs) have revolutionized the lighting industry. To improve the performance of white LEDs, phosphors having excellent luminescence properties are required. BaMgAl 10 O 17 (BAM) doped with Eu2+ is a candidate phosphor with blue emission for white LEDs. However, it has the disadvantages of low thermal stability and chromaticity coordinate deviation. Here, based on ionic couple substitution strategy, the co-substitution of Ba2+-Mg2+ in BAM: Eu2+ by K+-Al3+ until fully converted to KAl 11 O 17 :Eu2+ (KAO:Eu2+) was successfully achieved. The co-substitution leads to an improvement of luminescence thermal stability as a result of the interaction between Eu2+ ion and crystal defects. Moreover, the synthesis temperature (∼1350 °C) of KAO:Eu2+ is lower than that of BAM:Eu2+ (>1600 °C) and it exhibits better color purity than that of BAM:Eu2+ and small chromaticity coordinate deviation. A white LED device, fabricated using the KAO:Eu2+ phosphor as a blue component, exhibits better performance, and, accordingly, KAO:Eu2+ is a good blue-emitting candidate for phosphor-converted white LEDs. This study provides a practical guideline for improving the luminescence properties in the known system and developing materials with unique optical features. • The co-substitution of Ba–Mg in BAM:Eu by K–Al until fully converted to KAl 11 O 17 :Eu was achieved. • The co-substitution leads to an improvement of luminescence thermal stability. • The synthesis temperature of KAO:Eu2+ is lower than that of BAM:Eu2+. • KAO:Eu2+ exhibits better color purity and small chromaticity coordinate deviation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A controllable structural ordering is achieved in Na 1+ x Hf 2− x Sc x (PO 4) 3 :Eu series. • The PLQY values for all scandium-involved analogues are all higher than 90%. • Structural ordering guarantees the most thermally stable luminescence in NHS 0.3 :Eu. Exploring NASICON-type materials emerges the fully ordered NaHf 2 (PO 4) 3 compound. Its cation/vacancy distribution forms an absolutely structural ordering three-dimensional arrangement. Further preparing a solid solution following Na 1+ x Hf 2− x Sc x (PO 4) 3 :Eu (NHS x :Eu; 0.0 ≤ x ≤ 1.6) confirms all compounds are isostructural. Densely atomic-connected framework guarantees the efficient blue emission, which yields > 90% photoluminescence quantum yield (PLQY) for all scandium-substituted analogues, yet the existence of heavy amount of luminescence killer (Eu3+) limits the performance of NaHf 2 (PO 4) 3 :Eu as a luminescent phosphor. Moreover, a controllable structural ordering/disordering is achieved by varying x value, which is confirmed by Raman and 31P MAS NMR spectra. The structural ordering/disordering is crucial in determining structural rigidity. Consequently, despite the voids in the framework filled with sodium ions as x increases has positive contribution to the structural robustness, cation/vacancy ordered form still builds the most rigid structure for NHS 0.3 , as established by the NHS 0.3 composition possessing the highest Debye temperature within the scandium-involved analogues, which are extracted experimentally by the low temperature specific heat measurements. As such, NHS 0.3 :Eu has the best thermal stability across the x range, which keeps 90% of integrated intensity up to 203 ℃ compared with room temperature value. This work provides insight into the structural specialty of NASICON structure. [ABSTRACT FROM AUTHOR]

The luminescence property of phosphors plays an important role in the performance of phosphor-converted white light-emitting-diode (pc-WLED). In this paper, we report a simple energy-transfer (ET) strategy to enhance Tb3+ emission under near-UV excitation in Y 4 Zn 4 (SiO 4) 5 (YZS) doped with Ce3+/Tb3+ phosphor. The luminescence properties of YZS:Ce3+ based on crystal structure of YZS were investigated. The ET mechanism from Ce3+ to Tb3+ was also discussed in detail. The color of emitted light can be adjusted from blue to green by introducing Tb3+ ions into YZS:Ce3+. More importantly, the Tb3+ emissions under near-UV excitation are enhanced evidently, and the excitation spectrum for the Ce3+,Tb3+ co-doped phosphor matches well with the emission of near-UV chip. The selected green phosphor and commercial red, blue phosphors were coated on a 365-nm chip to fabricate a WLED device. The WLED shows an outstanding performance (R a = 93.5 and CCT = 4769 K), indicating that YZS:Ce3+,Tb3+ phosphors have potential applications in near-UV pc-WLED as a green-emitting component. • The relationship on Ce3 + luminescence and crystal structure of host. • Tb3 + emission is enhanced by energy transfer strategy. • An outstanding performance of WLED device is obtained. • YZS:Ce3 + ,Tb3 + has application in WLED as a green-emitting component. [ABSTRACT FROM AUTHOR]

A series of Ce3+ and/or Eu2+ doped T-phase orthosilicate Ba 1.2 Ca 0.8 SiO 4 (BCS) phosphors were synthesized by conventional solid state reaction. The as-synthesized samples were investigated by X-ray diffraction (XRD), photoluminescence spectroscopy, and fluorescence decay curve. The red shifts of emission peak were observed in Ce3+ and/or Eu2+ doped BCS phosphors. The possible rationalization for the red shift was discussed. The emission color for BCS:Ce3+, Eu2+ phosphors can be turned from deep blue to bluish green by varying Eu2+ concentration. The efficient energy transfer from Ce3+ to Eu2+ is responsible for this phenomenon. The energy transfer mechanism was validated and demonstrated to be a resonant type via a dipole–dipole interaction by using Inokuti–Hirayama model and Dexter's energy transfer theory. In addition, the thermal stability of the phosphors is also investigated. Furthermore, the quantum efficiency (QE) of Ba 1.15 Ca 0.8 SiO 4 :0.02Ce3+, 0.02Na+, 0.01Eu2+ phosphor was found to be 38.77%. Finally, to explore the practical applications of obtained compounds for indoor illumination, a white light-emitting-diode (LED) device which contained a n-UV chip, prepared phosphors, and green emitting and red emitting phosphors was packaged. The packaged white LEDs device can emit dazzling white light with satisfied color coordinate of (0.350, 0.335), R a (84), and correlated color temperature (4744 K). • Ce3+ and/or Eu2+ doped T-phase Ba1.2Ca0.8SiO4 phosphors were synthesized. • Efficiently energy transfer from Ce3+ to Eu2+ is confirmed. • Color tunable emissions from deep blue to bluish green are achieved. • T-phase Ba 1.2 Ca 0.8 SiO 4 :Ce3+,Eu2+ is a candidate phosphor for white LEDs. [ABSTRACT FROM AUTHOR]

Development of rare-earth-free phosphors is quite significant. It is well known that luminescence of Sn2+ depends strongly on the structure of the host crystal. The emission of Mn2+ is often very weak due to forbidden 4T 1 → 6A 1 transition. However, it can be enhanced by means of energy transfer. This work deals with the photoluminescence of calcite- and vaterite-type CaCO 3 doped with Sn2+, Mn2+ phosphors. The phosphor particles were prepared via a simple co-precipitation method. The phase purity of the synthesized particles was determined by X-ray powder diffraction. Scanning electron microscopy images were obtained to study the particle morphology. Photoluminescence properties were determined by recording the emission spectra and excitation spectra. Furthermore, the fluorescence lifetimes were recorded to investigate decay and energy transfer behavior of the samples. The emission colors of calcite-CaCO 3 :Sn2+ and vaterite-CaCO 3 :Sn2+ are different under 254 nm UV excitation, which is explained by the different coordination environment of Ca2+. For the Sn2+-Mn2+ co-doped samples, the emission intensity of Mn2+ becomes stronger than that of Mn2+ singly doped sample, which is attributed to Sn2+ → Mn2+ energy transfer. Inokuti-Hirayama model is used to analysis of the involved energy transfer mechanism. The color tone of the samples can be tuned in the visible spectral region through adjusting the Mn2+ doping concentration. Near cold white-light emission can also be achieved in a single host co-doped with Sn2+ and Mn2+. • The phosphors are rare-earth-free luminescent materials. • Stable vaterite-type CaCO 3 were prepared by a simple co-precipitation method. • PL of calcite- and vaterite-CaCO 3 :Sn2+ was studied based on crystal structure. • Mechanism of energy transfer from Sn2+ to Mn2+ was discussed. • Color tone of the samples can be tuned by changing Mn2+ concentration. [ABSTRACT FROM AUTHOR]

The new phosphors K3Gd5(PO4)6 doped with Eu3+, Ce3+, or Tb3+ and co-doped with Ce3+ and Tb3+ are prepared by solid state reactions of K2CO3, Gd2O3, NH4H2PO4, Eu2O3, CeO2, and Tb4O7 (600 °C for 2 h and 850 °C for 5 h). [ABSTRACT FROM AUTHOR]