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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]

A novel apatite structure phosphor Ca 9 La(PO 4 ) 5 (GeO 4 )F 2 :Dy 3+ (CLPGF:Dy 3+ ) with a hexagonal lattice in the P 6 3 / m space group was synthesized via a facile solid state technique. The crystal and fine local structure as well as their photoluminescence properties were investigated in detail. The CLPGF:Dy 3+ phosphor can absorb in the UV-vis spectral region of 290–475 nm and exhibit two intense emission bands centered at 485 and 580 nm, which ascribes to 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions of Dy 3+ , respectively. The concentration quenching of Dy 3+ emission occurs via the energy transfer among the nearest-neighbor ions and the corresponding quenching mechanism was verified to be the dipole-dipole interaction. The quantum efficiencies of the phosphors were examined to be 72.9% and its luminescence intensity at 150 °C decreases to 93.8% and 98.6% of the initial value at room temperature, which corresponds to 4 F 9/2 to 6 H 15/2 transition and 4 F 9/2 to 6 H 13/2 transition of Dy 3+ ions, respectively. Their interesting photoluminescence properties indicate that the CLPGF:Dy 3+ phosphor is a promising white-emitting candidate for w -LEDs applications. [ABSTRACT FROM AUTHOR]

Tm 3+ /Yb 3+ co-doped BaLa 2 ZnO 5 up-conversion (UC) phosphors were successfully synthesized by high temperature solid-state reaction method. The X-ray diffraction (XRD) results show that synthesized phosphor co-doped with 0.75% Tm/10% Yb has the optimum pure phase of BaLa 2 ZnO 5 among different co-doping concentrations. The structure of BaLa 2 ZnO 5 :0.75% Tm/10% Yb phosphor was refined by the Rietveld method and results show the decreased unit cell parameters and cell volume after doping Tm 3+ /Yb 3+ , indicating that Tm 3+ /Yb 3+ have successfully replaced La 3+ . Under excitation at 980 nm, Tm 3+ /Yb 3+ co-doped BaLa 2 ZnO 5 phosphors present bright blue emission near 478 nm generated by the 1 G 4 → 3 H 6 transition and weak red emissions around 653 nm and 692 nm generated by the 1 G 4 → 3 F 4 and 3 F 3 → 3 H 6 transitions of Tm 3+ , respectively. The UC luminescence properties of BaLa 2 ZnO 5 phosphors co-doped with different Tm 3+ /Yb 3+ concentrations were investigated, and the related UC mechanisms of Tm 3+ /Yb 3+ co-doped BaLa 2 ZnO 5 depending on pump power were studied in detail. [ABSTRACT FROM AUTHOR]

Up-conversion phosphors BaLa 2 ZnO 5 co-doped with Ho 3+ /Yb 3+ were synthesized by high temperature solid-state reaction method. The phase composition of the phosphors was characterized by X-ray diffraction (XRD). The structure of BaLa 2 ZnO 5 : 0.75% Ho/15% Yb phosphor was refined by the Rietveld method and results showed the decreased unit cell parameters and cell volume after doping Ho 3+ and Yb 3+ , indicating Ho 3+ and Yb 3+ have successfully replaced La 3+ . Under the excitation of 980 nm diode laser, the strong green and weak red up-conversion emissions centered at 548 nm, 664 nm and 758 nm were observed, which originating from 5 S 2 , 5 F 2 → 5 I 8 , 5 F 4 → 5 I 8 and 5 S 2 , 5 F 2 → 5 I 7 transitions of Ho 3+ ions, respectively. The optimum doping concentrations of Ho 3+ and Yb 3+ were determined to be 0.75% and 15%, and the corresponding Commission International de L'Eclairage (CIE) coordinates are calculated to be x =0.298 and y =0.692. The related UC mechanism of Ho 3+ /Yb 3+ co-doped BaLa 2 ZnO 5 depending on pump power was studied in detail. The results indicate that BaLa 2 ZnO 5 : Ho 3+ /Yb 3+ can be an effective candidate for up-conversion yellowish-green light emitter. [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]

Rare earth doped luminescent sensing materials as non-contact thermometers have attracted extensive research interests due to their wide applications in areas like military, medical care, aerospace, etc. How to expand the working temperature range and improve the sensitivity has become the focus. In this work, we synthesized a series of apatite-structured luminescent temperature sensors M 2 La 7.9 Ce 0.1 (SiO 4) 6 O 2 (M = Ca, Sr, Ba) via isomorphic substitution. By monitoring the differential changes of emission intensities from Ce3+ at the 7-coordinate and 9-coordinate site respectively when temperature varies, the real-time temperature can be determined. These materials were proven to possess the maximum absolute sensitivity up to 0.825 × 10−3 K−1, 2.63 × 10−3 K−1 and 4.33 × 10−3 K−1, respectively. Meanwhile interesting regular patterns were observed for their temperature sensitivities with the substitution of Ca, Sr and Ba. Furthermore, through studying the temperature sensitivity of Ba 2 La 8 (SiO 4) 6 O 2 : x Ce3+ samples with different concentrations, it was found that when the Ce3+ content was at the optimal doping concentration of 0.7, the absolute sensitivity of the sample reached 14.64 × 10−3 K−1 at 573 K. This finding has opened up a new avenue for designing fluorescent temperature sensors. Synopsis: In this work, Ce3+ were doped into a series of phosphor-structured matrices containing two cationic sites (7-coordinated Ce1 and 9-coordinated Ce2 sites) via the solid-state high-temperature method. Due to the different temperature dependencies of luminescence intensities between the two Ce3+ sites, their intensity ratio could be used for temperature calibration. [Display omitted] [ABSTRACT FROM AUTHOR]

The constructed high-efficient cyan-emitting phosphors establish a bifunctional platform involving high-color-quality lighting and anti-counterfeiting application. [Display omitted] • Ca 8 ZnY(PO 4) 7 :Eu2+ phosphors exhibited a broad cyan-emitting spectra (FWHM = 78 nm). • The quantum yield of Ca 8 ZnY(PO 4) 7 :Eu2+ phosphor is as high as 72.11 %. • The CRI value of warm w -LED devices was greatly enhanced from 83.9 to 90.5. • The transparent anticounterfeiting film held great potentials in packaging field. Constructing the broad-band emitting luminescent materials with high quantum yield is of great significance towards their widespread applications. Herein, series of Eu2+ activated, whitlockite-type Ca 8 ZnY(PO 4) 7 phosphors are developed towards bifunctional platform involving the white LED and anti-counterfeiting field. Benefiting from the typical 5d-4f transitions among Eu2+ ions, the broad asymmetric cyan-emission spectra (FWHM = 78 nm) is generated under 365 nm excitation with a highest quantum yield of ∼72.11 %. The optimal doping concentration of Eu2+ ions in the Ca 8 ZnY(PO 4) 7 host is determined as 4 % and the concentration quenching mechanism is mainly attributed to a dipole–dipole interaction. Impressively, after exploiting the newly discovered cyan-emitting phosphors Ca 8 ZnY(PO 4) 7 :Eu2+, the CRI value of as-prepared warm w -LED devices is remarkably enhanced from 83.9 to 90.5. Moreover, the w -LED exhibits an applicable correlated color temperature (CCT = 4176 K) and good color stability. Additionally, the transparent anticounterfeiting film is fabricated based on the highly efficient phosphors and soluble PVA, which presents anticounterfeiting performances due to their bright cyan emission upon UV light. Notably, their sustainability, excellent flexibility and foldability provide more possibilities applied for anticounterfeiting field. These results suggest the highly efficient phosphors Ca 8 ZnY(PO 4) 7 :Eu2+ are promising bifunctional luminescent platforms, for both high-color-quality lighting and anticounterfeiting applications. [ABSTRACT FROM AUTHOR]

A series of new luminescent emission-tunable phosphors Sr 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ , Tb 3+ with apatite structure have been synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence emission and excitation spectra, lifetime, as well as the effect of Tb 3+ concentration are investigated to characterize the resulting samples. The critical distance was calculated to be 8.26 Å by using the concentration quenching method. The intense green emission was observed in the Sr 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ , Tb 3+ phosphors on the basis of the efficient energy transfer from Ce 3+ to Tb 3+ with an efficiency of 68.55%. And a possible mechanism of the energy-transfer from Ce 3+ to Tb 3+ ion is also proposed. The results indicate that Sr 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ , Tb 3+ phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes because of the broad excitation in the near-ultraviolet range and the efficient green emission light. [ABSTRACT FROM AUTHOR]

SrIn2O4, which shows lower phonon energy than CaIn2O4, is not only a good photocatalyst but also can be an excellent up-conversion (UC) host to exhibits UC luminescence. In this work, Yb3+ and/or Er3+ doped SrIn2O4 phosphors were synthesized, and their UC luminescence properties were studied and compared with those in the CaIn2O4 host. The structure of SrIn2O4: 0.01Er3+ and SrIn2O4: 0.1Yb3+/0.01Er3+ samples were refined by the Rietveld method and found to that SrIn2O4: 0.1Yb3+/0.01Er3+ showed increasing unit cell parameters and cell volume, indicating In3+ sites were substituted successfully by Yb3+ and/or Er3+ ions. From the UC luminescence spectra and diffuse reflection spectra, Er3+-doped SrIn2O4 showed very weak luminescence due to ground state absorption of Er3+; Yb3+/Er3+ codoped SrIn2O4 presented strong green (550 nm) and red (663 nm) UC emissions which were assigned to energy transfer from Yb3+ transition 2F7/2→2F5/2 to the Er3+ transition 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2. Comparing with CaIn2O4, Yb3+/Er3+ codoped SrIn2O4 showed obvious advantages with higher UC luminescent intensity. The pumping powers study showed that UC emissions in Yb3+/Er3+ codoped SrIn2O4 were attributed to energy transfer of Yb3+→Er3+ with a two-photon process. The possible UC luminescent mechanism of Yb3+/Er3+-doped SrIn2O4 was discussed. [ABSTRACT FROM AUTHOR]

Abstract The supercapacitance performance of birnessite, which is a common layered manganese oxide mineral with the general formula of (Na, K, Ca) x (Mn4+, Mn3+) 2 O 4 ·1.5H 2 O, is greatly hindered by poor electrical conductivity, especially when the areal mass loading of the active materials is high enough for practical application. Heterogeneous atom doping is an effective way for improving the supercapacitance performance of birnessite. Herein, we mainly investigate the influence of Fe doping on the crystal structure, electronic structure and capacitance performance of birnessite [(Na, K) x (Mn4+, Mn3+) 2 O 4 ·1.5H 2 O] in detail by combining the experiments and theoretical calculations/simulations. It is found that Fe atoms mainly substitute the central trivalent Mn in [MnO 6 ] octahedral after doping without changing the crystalline phase of birnessite. Meanwhile, the particle size and surface area of Fe-doped birnessite continuously increase with the increase of the content of Fe dopant. On the other hand, the electronic conductivity of the doped birnessite firstly increases and then decreases with the increase of the Fe content due to the reduced indirect band gap and the increased number of the boundary/grain interfaces. Based on these results, the influences of Fe doping on the supercapacitance performance of birnessite electrode with very high areal mass loading of ∼10–12 mg cm−2 are elaborately discussed related to morphology, structure, electrical conductivity, and ion diffusion properties. Graphical abstract Image 1 Highlights • Fe (III) mainly substituted Mn (III) in [MnO6] octahedral after Fe doping. • Particle size decreased and surface area greatly increased after Fe doping. • The indirect band gap of Fe-doped birnessite calculated from DFT reduced. • 5 mol% Fe-doped samples showed the best capacitance performance. [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]

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]