Search

The development of novel narrow-band emitting phosphors with high efficiency and stability is of great significance for WLED backlights. In recent years, the research on Bi 3+ -activated narrow-band emitting phosphors has gained significant attention for developing novel phosphors for WLED backlight applications. This Frontiers article presents recent advances in Bi 3+ -activated narrow-band emitting phosphors, encompassing their coordination environment and photoluminescence properties. The latest advancements in Bi 3+ -activated narrow-band emitting phosphors are categorized into four types based on host materials: germanate, silicate, borate, and other hosts. Additionally, detailed discussions are provided on the challenges associated with developing novel Bi 3+ -activated narrow-band emitting phosphors and potential research directions for future work. Overall, the Bi 3+ -activated narrow-band emitting phosphors have demonstrated great potential for WLED backlights; however, significant efforts are still required to enhance their comprehensive performance in order to meet practical application requirements.

Despite extensive research on the photoluminescence properties of Bi 3+ ions, the origins of their emission and excitation bands remain elusive. Herein, we present a comprehensive analysis of the photoluminescence properties of Bi 3+ -activated LuXnGaO 4 (Xn = Mg, Zn), elucidating the underlying factors governing the intra-ionic and extra-ionic electronic transitions. By integrating crystal structure data and spectroscopic data analyses with semi-empirical formula calculations, the origins of excitation and emission states were elucidated. Moreover, the impact of alterations in chemical surroundings on the luminescence of Bi 3+ was investigated. Both LuXnGaO 4 :Bi 3+ phosphors exhibit three excitation peaks in the near ultraviolet region and display a broadband yellow emission. However, the luminous behavior of LuMgGaO 4 :Bi 3+ and LuZnGaO 4 :Bi 3+ differs due to variations in the band gap, bond length and neighboring atoms. It is anticipated that the investigation of Bi 3+ -activated gallates presents a promising avenue for advancing wide-band and long-wavelength emitting phosphors.

Developing optical thermometer phosphors with high sensitivity, high signal discriminability and strong fluorescence intensity is ongoing. A dual-emitting thermochromic phosphor, LiScSiO 4 :Ce 3+ , Tb 3+ , was successfully synthesized via solid-state reaction method. The crystal structure, electronic structure, luminescent performance and thermal luminescence behaviors as well as the luminescence mechanism of LiScSiO 4 :Ce 3+ , Tb 3+ were systematically investigated. Due to the energy transfer and different thermoluminescence behaviors between Ce 3+ and Tb 3+ , high relative sensitivity (2.2 % K -1 @473 K), excellent signal discriminability (5747 cm -1 ), outstanding temperature resolution (0.067 K) and good repeatability, as well as efficient emission at high temperatures were achieved based on the fluorescence intensity ratio of Ce 3+ and Tb 3+ , indicating its potential in ratiometric optical thermometer. Moreover, the excellent visualizing thermochromic enable LiScSiO 4 :Ce 3+ , Tb 3+ to be used as safety sign in variable temperature environment to monitor temperature distribution., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Developing nitridosilicate red phosphors under mild synthesis conditions is important for regulating the emission quality of white light-emitting diodes (WLEDs). Based on the thermodynamic theory and crystal structure chemistry for the synthesis of nitridosilicates, the Gibbs free energy variation of a hybrid system can be made more negative by reducing the proportion of Si 3 N 4 and increasing the proportion of M 2 N 3 and AlN, enabling the formation of new nitridosilicates under mild conditions. Therefore, a general chemical formula M x Si y Al z N k was proposed for the design of nitridosilicate red phosphors prepared under mild conditions, where M is an alkaline earth metal ion; x > y ; z ≥ y ; 1 ≤ y ≤ 3; x + 2 y = 3 n + 3; k - z = 2 n + 2; and n is a positive integer. Therefore, in this study, we successfully synthesized the nitridoalumosilicate red phosphor Ca 4 SiAl 3 N 7 :Eu 2+ at normal pressure and lower temperature (1350 °C). Under excitation with 460 nm blue light, the Ca 4 SiAl 3 N 7 :Eu 2+ phosphor efficiently emits red light at 645 nm and exhibits excellent thermal stability. The crystal structure and luminescence properties of Ca 4 SiAl 3 N 7 :Eu 2+ were investigated in detail. The results indicate that Ca 4 SiAl 3 N 7 :Eu 2+ exhibits strong potential for use in WLEDs. The design of nitridoalumosilicate red phosphors synthesized under mild conditions based on Gibbs free energy variation provides a new idea for the development of new nitride phosphors.

Owing to the broad application scope of phosphors for light and display, the development of narrow-band light-emitting phosphors has recently gained considerable research attention. In this study, a new type of narrow-band blue light-emitting phosphor, Rb 2 HfSi 3 O 9 :Eu 2+ , with a full width at half maximum (FWHM) of 64 nm was synthesized successfully. Upon the near visible ultraviolet (NUV) light excitation, the internal quantum efficiency of Rb 2 HfSi 3 O 9 :Eu 2+ was 68%. It also exhibited good thermal stability, which was higher than that of a commercial blue phosphor (BaMgAl 10 O 17 :Eu 2+ ) at 150 °C. The significant photoluminescence properties of Rb 2 HfSi 3 O 9 :Eu 2+ were found to be related to its robust crystal structure, which was investigated in detail. The results indicate that Eu 2+ -activated Rb 2 HfSi 3 O 9 is a promising phosphor for use in white light-emitting diodes.

Cyan phosphors have attracted considerable attention in recent years as an indispensable component for realizing full-spectrum lighting. In this study, a novel nitride-based cyan-emitting phosphor Ca2BN2Cl:Eu2+ was successfully prepared. Its crystal structure refined by the Rietveld refinement reveals that Ca2BN2Cl is formed by a tight host lattice and the edge-sharing Ca(N,Cl)4 tetrahedrons along with multiple crystallographic Ca sites for Eu2+ ions to occupy, which corresponds to its broad emission band. Under the near ultraviolet (NUV) light excitation, Ca2BN2Cl:Eu2+ emits a broad-band cyan light and its full width at half-maximum (FWHM) can reach 121 nm, which effectively compensates the "cyan cavity". The time-resolved photoluminescence (TRPL) spectra of Ca2BN2Cl:Eu2+ were investigated to expose the energy transfer between the multiple luminescent centers. Furthermore, the temperature-dependent spectra of Ca2BN2Cl:Eu2+ were measured to evaluate its thermal stability. All of the discussion and results reveal that Ca2BN2Cl:Eu2+ is a promising cyan phosphor for use in white light-emitting diodes to realize full-spectrum lighting.

A series of BaSr 2 Sc 4 O 9 and Ce 3+ -doped BaSr 2 Sc 4 O 9 phosphors were synthesized via the high temperature solid state reaction. Crystal structure information on BaSr 2 Sc 4 O 9 is first refined using the Rietveld method based on the XRD data, and it is assigned to the trigonal system with the R3 space-group. The photoluminescence properties were investigated in detail, including the emission and excitation spectra, site occupation, decay lifetime, thermal quenching, and quantum efficiency. There are three Ba 2+ /Sr 2+ sites and four Sc 3+ sites in this structure. The Ce 3+ ions in the 6-fold coordinated Sr 2+ /Ba 2+ sites show a near-ultraviolet-blue emission with a peak at around 407 nm under ultraviolet excitation. The Ce 3+ ions in Sc 3+ sites exhibit a bright broad orange-red emission with the peak at around 615 nm under near-ultraviolet and blue excitation. The energy transfer process between the different sites is demonstrated based on the spectral analysis, theoretical calculation, and decay lifetime variation. Under excitation of 345 nm, the energy transfer phenomenon and distribution of activator ions lead to the invalidation of part of the Ce 3+ ions, and then it causes a higher concentration quenching point. The participation of the energy transfer in the thermal quenching phenomenon causes the abnormal intensity variation, which is ascribed to the energy compensation by the increasing energy transfer efficiency at high temperature. The internal quantum efficiency is 45% under the 420 nm excitation wavelength. An excellent white light emitting diode lamp is obtained by fabricating BaSr 2 Sc 4 O 9 :Ce 3+ with BAM:Eu 2+ , β-sialon:Eu 2+ , and a 395 nm GaN chip; its CIE coordinate ( x, y), CCT, and Ra are (0.3708, 3463), 4023 K, and 84. These results reveal the correlation between energy transfer and luminescent property and provide a practical foundation to comprehend and adjust the photoluminescence performance.

In recent years, the rare-earth elements in white light-emitting phosphors have a problem of increased demand and high price. To overcome these disadvantages, defects have been considered to act as new efficient luminescent centers to replace rare-earth elements. In this work, a rare-earth free self-activated orange light emitting phosphor of single-phase magnesium boron nitride, Mg 3 BN 3 , was successfully designed and synthesized by a relatively simple solid-state reaction. Its crystal structure and electronic structure have been measured using Rietveld refinement on the basis of X-ray diffraction data and density functional theory (DFT). The results show that Mg 3 BN 3 crystallizes in a centrosymmetric hexagonal phase with plenty of N[double bond, length as m-dash]B[double bond, length as m-dash]N double bonds and has a direct bandgap. The SEM and TEM images and Raman spectra exhibit the sample's good dispersibility and great crystallinity. Under excitation at 397 nm, a broad emission band with orange light emission peaked at 617 nm can be obtained. It is speculated to result from the defect energy levels formed by vacancies, which can also lead to tunability of the emission peak at about 100 nm. The thermal quenching shows that Mg 3 BN 3 at 200 °C still has more than 40% of the initial intensity at room temperature. All these results indicate that the self-activated light emitting phosphors of Mg 3 BN 3 are a potential candidate for n-UV LED applications.

Aluminum oxynitride (AlON) was commonly used in functional ceramic materials, including phosphors for white light-emitting diodes (LEDs). In the current work, a new polymorph of AlON structure, single phase [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3 , has been devised and synthesized through the solid-state reaction at a rather low temperature of 1550 °C. Its structure has been calculated by the Rietveld refinement. The [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3 crystallizes in trigonal with lattice parameters of a = b = 3.0312 Å, c = 41.5758 Å, V = 330.83 Å 3 , respectively, and it is formed by Mg 2+ and Si 4+ ions replacing partical Al 3+ ions of Al 5 O 3 N 3 . The photoluminescence spectra of a series of Eu 2+ doped [Mg 1.25 Si 1.25 Al 2.5 ]O 3 N 3 show a tunable light ranging from cyan to orange with a full-spectrum-covered emission and a wide excitation band with two peaks located at 290 and 335 nm. This is resulted from the two possible sites offered by the cation substitution for Eu 2+ to occupy and thus broadening the emission spectra, which significantly enrich the monotonous luminescent properties of conventional AlON phosphors. Additionally, the energy transfer from one site to another has been identified using the decay curves and time-resolved emission spectra. The scanning electron microscopy and transmission electron microscopy characterization confirmed the sample's great crystallinity and the thermal stability with more than 85% of the initial intensity at 250 °C further indicates its potential in white LED applications.

In this work, reciprocal energy transfer between Mn 2+ and Eu 2+ ions in nitride SrAlSi 4 N 7 has been found and investigated in detail. In contrast to Mn 2+ - and Eu 2+ -activated oxide-based phosphors, the red light centered at 608 nm is ascribed to 4f-5d transitions of Eu 2+ ions and Mn 2+ -activated SrAlSi 4 N 7 emits a cyan light peaking at 500 nm. Additionally, the special broad excitation band of SrAlSi 4 N 7 :Mn 2+ centered at 362 nm has been covered by that of Eu 2+ ions ranging from 300 to 550 nm. The overlap of the energy level of Mn 2+ and Eu 2+ ions creates the conditions for reciprocal energy transfer between Eu 2+ and Mn 2+ ions. A series of SrAlSi 4 N 7 :0.002 Mn 2+ ,xEu 2+ (0≤x≤005) with tunable light emission have been synthesized and the decay curves of samples prove the reciprocal occurrence of the energy transfer between Mn 2+ and Eu 2+ ions. This mode of energy transfer not only prevents the loss of energy, but also improves the thermal stability, and the intensity of SrAlSi 4 N 7 :Mn 2+ ,Eu 2+ at 150 °C is still beyond 92 % of the initial intensity. The results provide a new mode of energy transfer, which is expected to reduce the drawbacks existing in energy transfer., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of nitride solid solutions (Ca 1-x Sr x ) 16 Si 17 N 34 :0.03Eu 2+ were successfully synthesized through the conventional solid-state method. The electronic crystal structure and photoluminescence characteristics were studied in detail. The excitation in the near-ultraviolet and blue regions of the samples shows a broad band in the 250-550 nm range, which can match well with the n-UV and blue lighting-emitting diode chips. Partial substitution of Ca 2+ by Sr 2+ results in a redshift emission, and the impacts of Sr content on the luminescence were researched in detail. Under 410 nm excitation, the phosphor exhibited tunable red emission from 616 to 653 nm by changing the concentration of Sr 2+ . Based on the crystal data, the emission can be fitted into three distinguished Gaussian components, which are attributed to the different Eu 2+ luminescence centers occupied in three disparate Ca 2+ (Sr 2+ ) lattice sites. The temperature quenching property of the phosphor was also investigated, and the good thermal stability of the phosphors was analyzed through the activation energy for thermal quenching. And the obtained CCT values from 2642 to 2817 K are suitable for a warm white light region. All the results indicated that the phosphors have possible application in the warm white light-emitting diodes.

Defect luminescence has been considered to be one of the most efficient ways to resolve the problem of the recent limited supply and increased demand for rare-earth elements. So, in this work, a novel self-activated long-persistent green-yellow and yellow emitting phosphors of α-Ca 3 B 2 N 4 and β-Ca 3 B 2 N 4 has been successfully synthesized by sample-pressuring sintering. The α-Ca 3 B 2 N 4 and β-Ca 3 B 2 N 4 all have a broad excitation band peaked at 300 and 350 nm and emit yellow-green light peaked at 550 nm and yellow light peaked at 575 nm respectively with the long afterglow properties. The crystal structures and electron structures of α-Ca 3 B 2 N 4 and β-Ca 3 B 2 N 4 have been investigated to show that orthorhombic β-Ca 3 B 2 N 4 corresponds to an ordered superstructure of cubic α-Ca 3 B 2 N 4 and the phase transformation between α-Ca 3 B 2 N 4 and β-Ca 3 B 2 N 4 would happen during the preparation process, which produces many intrinsic defects forming the luminescent center. The thermoluminescence (TL) curve shows that there are traps in the host lattice with the TL peak located at 310 K. The results indicate that α-Ca 3 B 2 N 4 and β-Ca 3 B 2 N 4 with the defect-related PL and LPL properties have potential applications in the LED and LPL used phosphors.

A near-UV excited phosphor, LiSr4(BN2)3:Eu(2+) (LSBN:Eu(2+)), was synthesized using a solid-state reaction at 800 °C. The crystal structure of LSBN had been refined and determined from the XRD profiles by the Rietveld refinement method, which belongs to the space group Im3[combining macron]m with the lattice constants a = b = c = 7.46112(23) Å. The excitation spectra of the LSBN:Eu(2+) phosphors were centered at around 370 nm and covered the range from 300 to 450 nm. Under 400 nm excitation, the emission spectra of the LSBN:Eu(2+) phosphors show a red emission centered at about 640 nm (FWHM ≈ 130 nm). And the energy transfer between the Eu(2+) ions is confirmed to arise from the electric dipole-dipole interactions. The nontypical emission blue-shift in the single luminescence center with increasing temperature luminescence properties is also investigated. The results indicate that LSBN:Eu(2+) could be conducive to the development of white light emitting diodes.

In this study, a series of novel single-phased white light-emitting phosphors, Sr(7.3-x/2-y/2)Ca(2.7-x/2-y/2)(PO4)6F2:xEu(2+),yMn(2+) (0 ≤ x ≤ 0.06, 0 ≤ y ≤ 0.9) (SCPF:xEu(2+),yMn(2+)), have been successfully prepared through a high temperature solid-state reaction. The crystal structure and photoluminescence have been measured and analyzed. The energy transfer mechanism is demonstrated to be a quadrupole-quadrupole interaction and the critical distance between the Eu(2+) and Mn(2+) has been calculated. Meanwhile, the efficiency η of the energy transfer from Eu(2+) to Mn(2+) can reach 76%. The excitation spectra monitored at 457 nm ranges from 290 nm to 400 nm. Under excitation at 365 nm, the emission spectra include two broad bands peaked at 458 nm and 570 nm. By changing the ratio of Eu(2+)/Mn(2+), the emission color can change from blue to white. Furthermore, our results give the Commission International de L'Eclairage (CIE) chromaticity coordinates for the white LED as (0.334, 0.307) and a correlated color temperature of 3982 K, which indicates that the SCPF:Eu(2+),Mn(2+) phosphor is a very promising candidate for use as a near ultraviolet (NUV) white light-emitting diode (WLED) phosphor.