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Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg 3 Gd 2 Ge 3 O 12 : Bi3+, Eu3+, the intensity has been remarkably improved by about 16% compared to the one without Bi3+ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu3+ substitution, the bond lengths between Bi3+ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu3+ totally replaced Gd3+ ions. In addition, Lu3+ and [SiO 4 ] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs. [ABSTRACT FROM AUTHOR]

A novel orange-red emitting orthosilicate phosphor LiGd 9 (SiO 4) 6 :Mn2+ (LGS:Mn2+) belongs to hexagonal lattice with P 6 3 / m space group was synthesized via solid-state method and the phase composition, crystal structure as well as luminescence properties were examined for potential application in near ultraviolet (n -UV) pumped white light emitting diodes (w -LEDs). The as-prepared LGS:Mn2+ phosphor exhibits three excitation bands peaked at 273, 312 and 410 nm, which corresponds to the transitions of Gd3+ from ground state 8S 7/2 to 6I 7/2 , 6P 7/2 and Mn2+ from ground state 6A 1 (6S) to the individual components of the multiplets [4A 1 (4G), 4E(4G)], respectively. Upon excitation at 312 nm, the phosphors display an intense broad orange-red emission peaked around 594 nm, which ascribed to the typical spin-forbidden transition (4T 1 (4G)-6A 1 (6S)) of the Mn2+ ions. The concentration quenching mechanism and average separation distance in conjunction with fluorescence decay times of Mn2+ ions in LGS:Mn2+ phosphor were discussed. The indispensable parameters for application in n -UV high-powered w -LEDs, such as the thermal quenching of photoluminescence and internal quantum efficiency of LGS:Mn2+ phosphor, have also been investigated in detail. The above results indicate that LGS:Mn2+ could play a key role as an orange-red emission for potential application in n -UV-based w -LEDs. • LiGd 9 (SiO 4) 6 O 2 :Mn2+ luminescent materials were synthesized successfully. • This phosphor have excellent thermal stability and emission efficiency. • High energy transfer efficiency could be obtained between Gd3+ and Mn2+ ions. [ABSTRACT FROM AUTHOR]

Highlights • The ET mechanism has been confirmed by the luminescence spectra and fluorescence decay curves. • The ET interaction mechanism was determined to be dipole–quadrupole interaction. • The emission color of as-prepared phosphor could be adjusted from green to yellow. Abstract The Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor with apatite structure has been successfully synthesized by high temperature solid-state reaction, and its luminescence properties as well as energy transfer mechanism has been investigated in detail. The energy transfer (ET) efficiency increases with increasing Sm3+ doping content, that was confirmed by the luminescence spectra and fluorescence decay curves of corresponding ions. The ET interaction mechanism was determined to be dipole–quadrupole interaction. The emission color of Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor could be adjusted from green (0.272, 0.489) to yellow (0.363, 0.395) area through controlling the dopant ratio of Tb3+/Sm3+. The above results indicate that the Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor has a great potential in white light-emitting diodes application. [ABSTRACT FROM AUTHOR]

Abstract The novel apatite-type phosphor Ca 9 Tb(PO 4) 5 (SiO 4)F 2 :Mn2+ (CTPSF:Mn2+) has been successfully synthesized and it demonstrated a potential for optical thermometry. The energy transfer process between Tb3+ and Mn2+ was of resonant type via a dipole-dipole mechanism based on the Inokuti–Hirayama theoretical model, and the energy transfer (ET) efficiency and ET rate were estimated. In view of the energy transfer behavior, a strategy, involving the use of Tb3+ and Mn2+ dual-emitting centers with different thermal quenching behavior, has been developed to achieve temperature sensitivity and good signal discrimination. The temperature dependence of the fluorescence intensity ratios (FIR) for the dual-emission bands peaking at 548 and 595 nm was studied in the range of 298–573 K under excitation of 377 nm ultraviolet light and the maximum relative sensitivity was approximately 1.92% K−1 at 423 K. It is expected that this preliminary study will provide an important advance in exploring novel ratiometric optical thermometry. Highlights • Novel apatite-type phosphor Ca 9 Tb(PO 4) 5 (SiO 4)F 2 was synthesized. • Energy transfer mechanism is estimated based on Inokuti–Hirayama model. • Non-contact thermometry was developed with a new inorganic material. • The maximum S r of the as-prepared phosphor was as high as 1.92% K−1. • This work provides an insight to design ratiometric optical thermometry. [ABSTRACT FROM AUTHOR]

Whitlockite-type structure phosphors have received extensive attention and research due to their adjustable chemical compositions in isomorphic compounds and providing rich crystal positions for doping activators. Ca 2.6 K 0.2 La 0.2 (PO 4) 2 whitlockite-type phosphors with Dy3+ singly doping and Dy3+, Eu3+ co-doping were prepared via high temperature solid-phase reaction, and the crystallographic characteristics, luminescence properties and temperature sensing performance were investigated in detail. The prepared phosphors are pure phase and both Dy3+ and Eu3+ enter into the matrix and produce blue, yellow and red emissions. The CCT values of the emitted light from Ca 2·6 K 0·2 La 0·2 (PO 4) 2 : Dy3+, Eu3+ phosphors increase with the Eu3+ concentration rises, changing from cold white light to warm white light. The integrated emission intensity of Dy3+ in the phosphor decreases with the change in the doping ratio of Dy3+ and Eu3+, causing by the energy transfer from Dy3+ to Eu3+. The Ca 2·6 K 0·2 La 0·13 (PO 4) 2 :0.06Dy3+, 0.01Eu3+ phosphor shows temperature sensing performance based on FIR technique, with the maximum relative sensitivity calculated to be 0.181% K−1. All the results reveal that the Ca 2·6 K 0·2 La 0·2 (PO 4) 2 : Dy3+, Eu3+ phosphors can be applied to w-LEDs and display devices, and can be used as a new type of optical thermometer. Dy3+/Eu3+ co-doped Ca 2·6 K 0·2 La 0·2 (PO 4) 2 phosphor applied for w-LEDS and temperature sensing. [Display omitted] • Single-phase luminescent materials Dy3+, Eu3+ co-doped Ca 2·6 K 0·2 La 0·2 (PO 4) 2 phosphor with whitlockite structure was synthesized for the first time. • The concentration quenching and energy transfer mechanisms were investigated. • The emission color of Ca 2·6 K 0·2 La 0·2 (PO 4) 2 : Dy3+, Eu3+phosphors changes from natural white light to warm white light with the increase of Eu3+ concentration. • The samples showed temperature sensing performance with maximum S a to be 2.06 × 10−3 K−1 and S r to be 0.181% K−1 under 303 K. [ABSTRACT FROM AUTHOR]

Ba 3 Sc(PO 4 ) 3 :Eu 2+ ,Tb 3+ (BSP:Eu 2+ ,Tb 3+ ) phosphors were successfully prepared via conventional high-temperature solid-state reaction, their luminescence properties as well as energy transfer mechanism have been investigated in detail. The energy transfer mechanism was proposed to be the dipole–quadrupole mechanism, and the energy transfer efficiency was also estimated. BSP:Eu 2+ ,Tb 3+ phosphors showed a broad emitting band centered at 518 nm and several sharp emission peaks, which were assigned to the 5 d →4 f allowed transitions of Eu 2+ ions and characteristic optical 5 D 4 – 7 F J ( J =6, 5, 4, and 3) transitions of Tb 3+ ions, respectively. The emission color of BSP:Eu 2+ , y Tb 3+ exhibited a controlled luminescence evolution in the green area owing to the Eu 2+ –Tb 3+ energy transfer process. [ABSTRACT FROM AUTHOR]

Emission-tunable phosphors Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ with apatite structure were synthesized by a solid-state reaction. The phase structure, photoluminescence (PL) properties, lifetimes and the PL thermal stability were investigated, respectively. The phosphor exhibited an asymmetric broad-band blue emission (Ce 3+ ) with peak at 403 nm and the line-type green emission with peak at 543 nm (Tb 3+ ). The varied color of the phosphors from blue to green can be achieved by properly tuning the relative ratio of Ce 3+ /Tb 3+ through the energy transfer from Ce 3+ to Tb 3+ ions. The critical distance was calculated to be 8.78 Å by using the concentration quenching method. When the temperature turned up to 150 °C, the emission intensity of Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ phosphor was 77% of its initial value at room temperature, which indicated the good thermal stability of the sample. All the properties indicate that the Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ phosphor has potential application of color-tunable w -LEDs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Near-infrared emitting phosphors LaOCl:Nd3+/Yb3+ were prepared. [•] LaOCl:Nd3+/Yb3+ samples show strong near-infrared emission lines in the region of 1060–1150nm and 980–1050nm. [•] The possible energy transfer mechanism between Nd3+ and Yb3+ was discussed. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) commonly undergoes doping with various dopants, leading to the emergence of new properties. In this study, HAP is co-doped by terbium (Tb) and europium (Eu) to impart HAP with photoluminescent properties. By controlling the Tb3+ amount to 7.5 × 10−5 mol unchanged, it is observed that when the doping amount of Eu3+ reaches 4.0 × 10−5 mol, the band gap measures 3.919 eV, with maximum fluorescence intensity. Notably, a dipole-dipole energy transfer type from Tb3+ to Eu3 was identified during this process. Concentration quenching occurs when the Eu3+ amount exceeds 4.0 × 10−5 mol. In addition, the Tb3+ and Eu3+ co-doped HAP demonstrates excellent thermal stability and a more comprehensive emission wavelength range than Tb3+-doped HAP or Eu3+-doped HAP. Considering these properties, Tb3+ and Eu3+ co-doped HAP phosphor and aramid/polyphenylene sulfide (ACFs/PPS) fiber paper are organically compounded, resulting in functional fabrics with excellent low-temperature stability. These available fabrics are made of luminescent crystals and fibers can be applied in fields such as high-performance textile testing. Notably, when a specific laser irradiates the damaged area of the textile, fluorescence is not detected by the detector. Moreover, Tb3+ and Eu3+ co-doped HAP has also been shown to be used in the light-emitting diode (LED) to produce the HAP-LED that emits warm white light without commercial phosphors. That expands the application of HAP in anti-counterfeiting, flexible wearables, high-performance textile testing, and semiconductor devices. The color-tunable Tb3+ and Eu3+ co-doped HAP is prepared by hydrothermal synthesis co-precipitation. The energy transfer process between Tb3+ and Eu3+ is proved and the application possibility of Tb3+ and Eu3+ co-doped HAP in fluorescence anti-counterfeiting and LED is discovered. [Display omitted] • The energy transfer mechanism of Tb3+ and Eu3+ in HAP was studied. • By controlling the doping amount of Eu3+, the fluorescence color of Tb3+ and Eu3+ co-doped HAP was tunable. • It expands the application of hydroxyapatite in fluorescent anti-counterfeiting and LED. • HAP exhibited excellent stability when combined with fibers for anti-counterfeiting applications. • The LED emitting bright white light was prepared by using Tb3+ and Eu3+ co-doped HAP without commercial phosphor. [ABSTRACT FROM AUTHOR]

Abstract A set of Eu3+, Dy3+ and Tb3+ doped novel scheelite-type LiCaGd(WO 4) 3 (LCGW)-based phosphors was prepared via a conventional solid-state reaction method. The X-ray diffraction (XRD), transmission electron microscopy (TEM) analysis, characteristics of luminescence, PL thermostability, decay lifetimes, as well as CIE coordination were investigated to characterize the as-prepared samples in detail. The XRD analysis indicated that the Eu3+, Dy3+ and Tb3+ ions were incorporated into the LCGW host lattice. Under the ultraviolet radiation, the characteristic emission lines of Eu3+ (5D 0 –7F 2), Dy3+ (4F 9/2 –6H 13/2) and Tb3+ (5D 4 –7F 5) ions were observed. The Eu3+ and Tb3+ single-doped LCGW fluorescent powders showed bright red and green emissions, respectively, without concentration quenching. As well as the Dy3+ doped LCGW phosphors radiate a strong yellow light at optimal Dy3+ concentration 0.08 mol. The efficient energy transfer phenomenon was observed for the Eu3+/Dy3+ and Tb3+/Dy3+ ions. The emission color of the LCGW: x Tb3+/0.08Dy3+ samples was tuned from yellow (0.4074, 0.4727) to green (0.3604, 0.5521) via adjusting the Tb3+ concentration. The emission color of LCGW: y Eu3+/0.08Dy3+ can be tuned from yellow (0.491, 0.3856) to red (0.5694, 0.3512) by variation of the Eu3+/Dy3+ ratio. Additionally, the thermal stability of the luminescence in the LCGW phosphors doped by Eu3+, Tb3+, Dy3+ ions was studied. The results verified that the LCGW:Ln3+ (Ln = Tb, Eu, Dy) phosphors are promising for applications in white LEDs. [ABSTRACT FROM AUTHOR]

Abstract A series of reddish-emitting apatite-type phosphor LiGd 9 (SiO 4) 6 O 2 :Sm3+ was prepared by using an appropriate solid-state method. The photoluminescence (PL), photoluminescence excitation (PLE) spectra, and decay times of the samples were characterized to investigate the photoluminescence properties for application in white light-emitting diodes (w -LEDs). The photoluminescence investigations showed that LiGd 9 (SiO 4) 6 O 2 :Sm3+ phosphor emitted reddish emission, which ascribed to the transitions of the Sm3+ from the 4G 5/2 excited state to the 6H 5/2 , 6H 7/2 , and 6H 9/2 states, respectively. The critical quenching concentration of Sm3+ in LiGd 9 (SiO 4) 6 O 2 phosphors were determined to be about 3 mol%. Moreover, the spectroscopic data and fluorescence decay dynamics indicate that the energy transfer from Gd3+ to Sm3+ ions takes place in LiGd 9 (SiO 4) 6 O 2 : Sm3+ phosphor. All the results indicated that the LiGd 9 (SiO 4) 6 O 2 : Sm3+ phosphor could efficiently assimilate the near ultraviolet (n -UV) light and act as a suitable warm light candidate for n -UV w -LEDs. [ABSTRACT FROM AUTHOR]

Currently, the application potential of Cr3+ doped near-infrared (NIR) fluoride phosphors excited by blue light is promising. However, the development of near-infrared fluoride phosphors with wider emission bandwidth remains a challenge. Herein, we employed the hydrothermal method to prepare K 2 NaCrF 6 :Fe3+ phosphors. Upon excitation at 432 nm, the K 2 NaCrF 6 :xFe3+ phosphors exhibited broad near-infrared emission, with the main peak ranging from 752 nm to 780 nm. As the Fe3+ concentration increased, the luminescence intensity of the K 2 NaCrF 6 :xFe3+ phosphor decreased, accompanied by a redshift in the emission band and an increase in the full width of the emission spectrum half-peak. These changes can be attributed to the dipole-dipole interaction, specifically the energy transfer between Fe3+ and Cr3+, leading to the 4T 2 (4F) → 4A 2 (Cr3+) and 4T 1 (4G) → 6A 1 (6S) (Fe3+) transitions. • K 2 NaCrF 6 :Fe3+ phosphors display application potential for near-infrared (NIR) fluorescence when excited by blue light. • The developed phosphors exhibit a broad near-infrared emission bandwidth (752–780 nm) under 432 nm excitation. • Increasing Fe3+ concentration leads to redshift and broadening of the emission spectrum. • Luminescent changes are attributed to dipole-dipole interactions and efficient energy transfer. • Cr3+ and Fe3+ enables synchronous excitation processes, offering versatility for applications in spectroscopy. [ABSTRACT FROM AUTHOR]

Rare earth ion doped fluorescent powder, as a key material for the application of white light-emitting diodes (w-LEDs), green components often face the problem of poor thermal stability. Developing fluorescent powders with excellent thermal stability is of great significance. This article synthesized a series of Gd 5 Si 2 BO 13 :Tb3+ blue phosphors and non rare earth Bi3+ ion doped Gd 5 Si 2 BO 13 :Tb3+ green phosphors using a high-temperature solid-phase method. The phase structure and photoluminescence characteristics of the sample were analyzed in detail through XRD, excitation and emission spectra, as well as attenuation curves. The energy transfer from Bi3+ to Tb3+ was studied and confirmed through photoluminescence spectra and lifetime decay curves. Research has shown that the addition of Bi3+ significantly enhances the emission intensity of Tb3+ in the near ultraviolet range, and tunes the emission color of Gd 5 Si 2 BO 13 :Bi3+ and Tb3+ from blue to green, attributed to the energy transfer from Bi3+ to Tb3+. In addition, the addition of Bi3+ increased the thermal stability of single doped fluorescent powder Gd 5 Si 2 BO 13 :0.55Tb3+ from 88.21 % to 92.82 % at 150 °C, proving that the Gd 5 Si 2 BO 13 :Bi3+ and Tb3+ samples have good thermal stability. This study not only deepens our understanding of the new main material Gd 5 Si 2 BO 13 , but also provides a reference for the development of green phosphors with excellent thermal stability. [Display omitted] • A series of Gd 5 Si 2 BO 13 :Bi3+, Tb3+ phosphors were successfully synthesized. • The co-doped Gd 5 Si 2 BO 13 :Bi3+, Tb3+ phosphors have excellent emission intensity and thermal stability. • The Gd 5 Si 2 BO 13 :Bi3+, Tb3+ green phosphors is promising for use in high-power LED lighting devices and backlight displays. [ABSTRACT FROM AUTHOR]

Near-infrared excited up-conversion phosphors of RE 3+ /Yb 3+ (RE = Ho, Tm) co-doped SrIn 2 O 4 were synthesized by a solid-state reaction method. X-ray diffraction analysis revealed the phase composition of those samples, and the up-conversion spectroscopic properties were studied in terms of up-conversion emission spectra. Under 980 nm near-infrared laser excitation, strong green emission with the peak at 546 nm was observed in SrIn 2 O 4 : Ho 3+ /Yb 3+ , which can be assigned to the characteristic 5 S 2 ( 5 F 4 ) → 5 I 8 transition of Ho 3+ . Furthermore, SrIn 2 O 4 : Tm 3+ /Yb 3+ showed bright blue emission with the peak at 486 nm, which is associated with the 1 G 4 → 3 H 6 transition of Tm 3+ . The UC power studies indicated that the luminescence of SrIn 2 O 4 : Ho 3+ /Yb 3+ and SrIn 2 O 4 : Tm 3+ /Yb 3+ are attributed to two-photon and three-photon process, respectively. The possible UC luminescence mechanism and energy transfer in SrIn 2 O 4 : RE 3+ /Yb 3+ were discussed. [ABSTRACT FROM AUTHOR]

The lanthanide-doped fluorescence intensity ratio (FIR) temperature measurement technology for detecting inaccessible objects has attracted the attention of many scholars. In fact, FIR technology can achieve high-precision and non-contact temperature measurement, which is widely used in the biomedical and industrial fields, among others. In this study, novel pyroxene-type CaScAlSiO 6 :Tb3+/Sm3+ ceramics (CSAC) were synthesized using the traditional high-temperature solid-phase method, with the crystal structure, energy transfer mechanism, and optical behavior of the ceramics subsequently studied in detail. The use of 5D 4 →7F 5 and 4G 5/2 → 6H 7/2 (I 544nm /I 602nm) energy level transitions as an optical thermometer has great potential, with the maximum absolute and relative sensitivity of the sensor found to be 0.1403 K−1 and 1.65%K−1, respectively. In addition, the material was cycled three times in the temperature range of 77–287 K and demonstrated a particularly high degree of credibility, with the luminous intensity having a particularly small effect on the temperature changes. Overall, the results indicate that the green-light-emitting CSAC:0.08Tb3+/0.01Sm3+ ceramic has great potential for use in optical cryothermometers. [ABSTRACT FROM AUTHOR]

Samarium (III) doped fluorapatite phosphors La 6- x Ba 4 (SiO 4 ) 6 F 2 : x Sm 3+ (LBSF: Sm 3+ ) were synthesized for the first time, via the conventional high-temperature solid-state method in the air atmosphere. The samples were measured by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy, i.e. emission and excitation spectra, as well as luminescence decay curves. The as-prepared samples can be excited in the range from 300–500 nm, centered at 404 nm. Photoluminescence measurements showed the emission spectra are composed of four sharp peaks characteristic of Sm 3+ ions, at about 565, 603, 650 and 711 nm. The critical concentration for quenching of Sm 3+ ions in the LBSF matrix is about 0.12 mol. According to the Dexter's theory, the mechanism of energy transfer between Sm 3+ ions was considered to be dipole-quadrupole (d-q) interactions, with the critical distance calculated by the concentration quenching method to 9.89 Å. Moreover, the temperature-dependent emission spectra showed that the as-prepared phosphors have good thermal stability, with an activation energy of about 0.161 eV. Finally, according to the CIE coordination, the phosphor exhibited reddish-orange emission. Thanks to the mentioned favorable structural and optical properties, the Sm 3+ -doped La 6 Ba 4 (SiO 4 ) 6 F 2 phosphors have a potential application character, for the near ultraviolet white light emitting diodes. [ABSTRACT FROM AUTHOR]

LED occupies a broad market due to its many advantages as a fourth-generation solid-state light source. However, single-component white LED generally has the disadvantages of high coloring temperature, low thermal stability, and low luminous efficiency. In order to solve these problems, Gd 5 Si 2 BO 13 :Dy3+,Eu3+ was prepared by a high temperature solid state method using a newer borate matrix based on Gd 5 Si 2 BO 13. A colour-tunable warm white phosphor was achieved by energy transfer between Dy3+ and Eu3+. The crystal structure, luminescence characteristics, thermal stability of luminescence, fluorescence lifetime and energy transfer mechanism were systematically studied, and the samples obtained had excellent luminescence performance. Its thermal stability of 150 °C luminescence was 83.77%. By adjusting the ratio of Eu3+, its color changes from cool white light to warm white light and finally moves to red light. Its corresponding color temperature can be adjusted to a range of 5475k∼2128 K. The packaging w-LED application test and the application test of colorless fluorescent anti-counterfeiting printing ink were carried out, and both showed excellent performance. This is the first time that Dy3+ and Eu3+ have been studied in Gd 5 Si 2 BO 13 , further understanding the newer substrate Gd 5 Si 2 BO 13 , and promoting the application of single-component warm white LED. Therefore, Gd 5 Si 2 BO 13 :Dy3+,Eu3+ have good market application prospects. [Display omitted] • Through the energy transfer between Dy3+ and Eu3+, Gd 5 Si 2 BO 13 :Dy3+/Eu3+ shows excellent Warm white light performance. • The phosphor showed good luminescence thermal stability, UV stability and wet resistance stability. • The color temperature of the sample was adjusted from 5475K to 2128K by adjusting the doping concentration of Eu3+. • The LED application test with Gd 5 Si 2 BO 13 :Dy3+,Eu3+ package shows good performance. [ABSTRACT FROM AUTHOR]

Developing color-tunable phosphors via the introduction of co-doping activators and sensitizers to the host with energy transfer processes has been a state-of-the-art topic for a long time. In this work, novel emission-tunable oxyapatites-type Ba 10 (PO 4 ) 6 O:Eu 2+ ,Tb 3+ /Li + phosphors were prepared via a high temperature solid state reaction for the applications in white light emitting diodes ( w -LEDs) with higher color rendering index. Tunable colors from blue to green can be realized in the Ba 10 (PO 4 ) 6 O:Eu 2+ ,Tb 3+ /Li + by varying the relative ratios of Eu 2+ to Tb 3+ , showing good absorption in the range of 230–400 nm. The energy transfer mechanism from Eu 2+ to Tb 3+ ions was demonstrated to be a quadrupole-quadrupole interaction by combining the Inokuti-Hirayama (I H) model and Reisfeld's approximation. Importantly, a prototype white lamp was packaged by mixing Ba 9.83 (PO 4 ) 6 O: 0.03Eu 2+ , 0.07Tb 3+ , 0.07Li + and commercial red phosphor CaAlSiN 3 : Eu 2+ , and the lamp exhibits a higher color rendering index (Ra = 92 and R9 = 56) and warm correlated color temperature of 4361 K for the actual application. Better luminescent properties compared to commercial Y 3 A l5 O 12 :Ce 3+ -based w -LEDs, indicating that Ba 10 (PO 4 ) 6 O: Eu 2+ , Tb 3+ /Li + phosphors are emerging as potential phosphor-converted w -LEDs. [ABSTRACT FROM AUTHOR]

Tb 3+ -Sm 3+ co-doped Sr 9 Gd(PO 4 ) 5 (SiO 4 )F 2 (SGPSF) phosphors were prepared through a solid-state reaction, and their luminescence properties as well as energy transfer mechanism have been investigated in detail. The SGPSF:Tb 3+ , Sm 3+ phosphors system could be efficiently excited at wavelengths ranging from 200 to 500 nm, which is well matched with the spectra of near ultraviolet chips. The emission of SGPSF:Tb 3+ , Sm 3+ phosphor covers the entire visible region with sharp peaks in the blue, green, and red regions. The emission color of SGPSF:Tb 3+ , Sm 3+ could be adjusted from green (0.275, 0.378) to red (0.519, 0.295) by controlling the doping content of Sm 3+ /Tb 3+ . [ABSTRACT FROM AUTHOR]

Tb 3+ –Sm 3+ co-doped Ba 3 NaLa(PO 4 ) 3 F phosphors with apatite structure have been prepared by a high temperature solid-state reaction, and their luminescence properties have been investigated in detail. The energy transfer (ET) mechanism was verified as the dipole–quadrupole mechanism, and the ET efficiency as well as the critical distance is also estimated. As a result of fine-tuning of the emission composition of the Tb 3+ and Sm 3+ ions, tunable luminescence properties can be realized by combining the emission of Tb 3+ and Sm 3+ in a single host lattice under UV light excitation. The emission color of the obtained phosphors can be modulated from green to yellow by controlling the doping content of the Sm 3+ ions with the fixed Tb 3+ content. Additional, as the temperature increases from RT to 150 °C, the PL intensities of Ba 3 NaLa 0.7 (PO 4 ) 3 F:0.10Tb 3+ ,0.20Sm 3+ decreased to 80.4% and 78.6% of the initial PL intensity, corresponding to the intensity of transition of Sm 3+ and transition of Tb 3+ in the Ba 3 NaLa 0.7 (PO 4 ) 3 F:0.10Tb 3+ ,0.20Sm 3+ phosphor, respectively. These results indicate the series of Ba 3 NaLa 1− x − y (PO 4 ) 3 F: x Tb 3+ , y Sm 3+ phosphors can be acted as a good candidate for the application in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Single-phase La 6 Sr 4 (SiO 4 ) 6 F 2 : Ce 3+ , Tb 3+ samples with apatite-like structure have been synthesized via solid-state reaction method. The phase structure, luminescence properties, lifetime, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples. Effective energy transfer occurs from Ce 3+ to Tb 3+ in La 6 Sr 4 (SiO 4 ) 6 F 2 , which shows more intense Blue-Green light under UV light excitation. In addition, a possible mechanism of the energy-transfer from Ce 3+ to Tb 3+ ion is also proposed. The critical distance R C of Ce 3+ to Tb 3+ ions in La 6 Sr 4 (SiO 4 ) 6 F 2 host was calculated to be 11.878 Å. All the results indicate that La 6 Sr 4 (SiO 4 ) 6 F 2 :Ce 3+ , Tb 3+ phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A series of Eu 2+ and Eu 2+ /Tb 3+ co-doped Ba 3 GdNa(PO 4 ) 3 F phosphors have been synthesized via a high temperature solid-state reaction. The relative intensity of PL spectra of Ba 3 GdNa(PO 4 ) 3 F: x Eu 2+ increases with increasing x value, and reaches a maximum at x =0.04. Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors exhibit a broad excitation band ranging from 220 to 450 nm, which matches perfectly with the characteristic emission of n -UV light-emitting diode (LED) chips. Upon 365 nm excitation, the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors show two dominating bands peaked at 466 and 543 nm, which are assigned to the 4f 7 →4f 6 5d 1 transition of the Eu 2+ ions and the 5 D 4 → 7 F 5 transition of the Tb 3+ ions, respectively. In view of the energy transfer mechanism between Eu 2+ and Tb 3+ , the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ emission color can adjust from blue to green, and their chromatic coordinates ( x , y ) vary from (0.16, 0.135) to (0.254, 0.398). The critical distance was also calculated to be 16.90 Å. The above results indicate that the Ba 3 GdNa(PO 4 ) 3 F: Eu 2+ , Tb 3+ phosphors are a candidate for blue–green components in the application of n -UV w -LEDs. [ABSTRACT FROM AUTHOR]

Cryolite was considered to be an ideal up-conversion host material due to its low phonon energy, which can effectively suppress the radiation-free transition process of excited state energy levels. In the present paper, a novel up-conversion material K 3 YF 6 :Ho3+, Yb3+ with cryolite structure was prepared successfully using a high-temperature solid state method. The up-conversion luminescence properties of K 3 YF 6 doped with different Ho3+/Yb3+ doping ratio were investigated and the optimal doping ratio were confirmed in this system. Under 980 nm excitation, Ho3+/Yb3+ co-doped K 3 YF 6 revealed a strong green emission at the 541 nm, 549 nm and a weak red emission peaking at 666 nm, corresponding to the 5F 4 , 5S 2 →5I 8 and 5F 5 →5I 8 transitions of Ho3+, respectively. All the red and green up-conversion emission of K 3 YF 6 :Ho3+, Yb3+ belong to two-photon process and energy transfer from Yb3+ to Ho3+ simultaneously. Additionally, to understand the energy transfer and electronic transition process of the red and green light emitted, the possible luminescence mechanism were also analyzed in this paper. All the results indicate that Ho3+/Yb3+ co-doped K 3 YF 6 have potential application value in green up-conversion luminescent materials. • Single-phase up-conversion luminescent materials K 3 YF 6 : Ho3+,Yb3+ with cryolite structure were obtained for the first time. • The up-conversion luminescence properties and mechanism of the as-prepared samples were analyzed under excitation of 980 nm. • Two-phonon up-conversion phenomenon was confirmed. [ABSTRACT FROM AUTHOR]

In this paper, K 3 ScF 6 :Yb3+, Tm3+ phosphor with a cubic cryolite phase were prepared by means of high-temperature solid-state method. The crystal structure and up-conversion luminescence properties of Tm3+ and Yb3+ co-doped K 3 ScF 6 were investigated in detail. Scanning electron microscope (SEM), energy disperse spectroscopy (EDS), elemental mapping and X-ray photoelectron spectroscopy (XPS) were used to analyze the elements composition, elemental distribution and valence states of samples. Under an excitation wavelength at 980 nm, all the samples displayed blue and red emission. When gradually increasing the concentration of Tm3+ in K 3 ScF 6 :0.2 Yb3+, Tm3+ and Yb3+ in K 3 ScF 6 : 0.01 Tm3+, Yb3+, the emission intensity of the samples appeared obviously concentration quenching effect, and the optimum concentration of Tm3+ and Yb3+ were confirmed to 0.01 and 0.20 mol%. Additionally, the effect of pump power on up-conversion emission intensity and the energy transfer mechanism between the Tm3+ and Yb3+ in these samples were analyzed in detail. • Single-phase Tm3+/Yb3+ co-doped K 3 ScF 6 with cryolite structure were synthesized for the first time. • Up-conversion properties of K 3 ScF 6 : Yb3+, Tm3+ were studied. • Mechanism of up-conversion was analyzed. [ABSTRACT FROM AUTHOR]