Synthesis and luminescence properties of broad band greenish-yellow emitting LnVO4:Bi3+ and (Ln1, Ln2)VO4:Bi3+ (Ln=La,Gd and Y) as down conversion phosphors

Ln_0.97VO₄:Bi_0.03³⁺ and (Ln1_0.5, Ln2_0.5)_0.97VO₄:Bi_0.03³⁺ (where Ln=La, Gd and Y) down conversion (DC) phosphors have been synthesized by a novel co-precipitation technique followed by heat-treatment. The influence of lanthanide host composition on crystal structure, luminescence and pertinent optical properties have been investigated by various spectroscopic techniques: XRD, SEM, FT-IR and PL. The produced phosphors have exhibited an intense greenish-yellow emission, upon UV-irradiation. A broad band excitation (280–350 nm) ascribed to ¹S₀→³P₁ and an intense broad greenish-yellow emission band (400–700 nm) attributed to ³P₁→¹S₀ transition, owing to Bi³⁺ ions have been observed. PL spectra revealed that the phosphors with Gd – containing host has exhibited a better luminescence among the others. The luminescence intensity sequence in descending order was as follows: GdVO₄→(Gd, Y)VO₄→(La, Gd)VO₄→(La, Y)VO₄→YVO₄→LaVO₄: Bi³⁺. These phosphors can efficiently convert the UV-photons in a broad range from 280–350 nm of feckless UV-rays into the absorbable visible emission for c-Si solar cells, based on the spectral matching phenomena. In view of the better fluorescence and pertinent optical properties, the phosphor with composition Gd_0.97VO₄: Bi_0.03³⁺ is a suggestible sought UV-absorbing spectral converter, in its thin transparent DC form for c-Si solar cells for better harvesting the solar energy.     

Down-conversion from Er3+-Yb3+ codoped CaMoO4 phosphor: A spectral conversion to improve solar cell efficiency

The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er³⁺ and Yb³⁺ in CaMoO₄:Er³⁺, Yb³⁺ phosphors. We have successfully synthesized a series of Er³⁺ doped and Yb³⁺ codoped CaMoO₄ phosphors by hydrothermal method. The down-conversion of Er³⁺-Yb³⁺ combination with CaMoO₄ phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er³⁺ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to ⁴S_3/2→⁴I_15/2 transition. The addition of Yb³⁺ into Er³⁺ doped CaMoO₄ attribute an emission at 980 nm due to ²F_5/2→²F_7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er³⁺ to Yb³⁺ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb³⁺ ion. The lifetime measurement also reveals the energy transfer from Er³⁺ to Yb³⁺ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

YBO3: Ce3+, Yb3+ based near-infrared quantum cutting phosphors: Synthesis and application to solar cells

Ce³⁺ and Yb³⁺ co-doped YBO₃ phosphors were facilely fabricated by a hydrothermal method. The investigations reveal that hexagonal YBO₃: Ce³⁺, Yb³⁺ nanoparticles aggregate to form cyclic structure after annealing at 900 °C. An efficient near-infrared (NIR) quantum cutting phenomenon involving the emission of two NIR photons (971 nm) for each ultraviolet (UV) photon (360 nm) absorbed is observed based on the cooperative energy transfer (CET) from Ce³⁺ to Yb³⁺ in YBO₃ with a CET efficiency of 41.9%. Moreover, YBO₃: Ce³⁺, Yb³⁺/SiO₂ films with anti-reflection and NIR quantum cutting abilities were prepared by dip-coating method. The as prepared composite films can convert UV photons into NIR photons between 950 nm and 1050 nm, which well matched with the spectral response of the silicon-based solar cell. The experimental results indicate that the photoelectric conversion efficiency of silicon solar cell can be effectively improved by assembling the YBO₃: Ce³⁺, Yb³⁺/SiO₂ bi-functional film, and the corresponding conversion efficiency is about 0.521% higher than the pure glass and 0.252% higher than the pure SiO₂ anti-reflection (AR) film. In a word, this work provides a simple strategy to develop optical films with AR and NIR quantum cutting abilities for solar energy conversion.     

Concentration effects on the upconversion luminescence in Ho3+/Yb3+ co-doped NaGdTiO4 phosphor

Ho³⁺/Yb³⁺ co-doped NaGdTiO₄ phosphors were synthesized by a solid-state reaction method. The upconversion (UC) luminescence characteristics excited by 980 nm laser diode were systematically investigated. Bright green UC emission centered at 551 nm accompanied with weak red and near infrared (NIR) UC emissions centered at 652 and 761 nm were observed. The dependence of UC emission intensity on excitation power density showed that all of green, red and NIR UC emissions are involved in two-photon process. The UC emission mechanisms were discussed in detail. Concentration dependence studies indicated that Ho³⁺ and Yb³⁺ concentrations had significant influences on UC luminescence intensity and the intensity ratio of the red UC emission to that of the green one. Rate equations were established based on the possible UC mechanisms and a theoretical formula was proposed to describe the concentration dependent UC emission. The UC luminescence properties of the presented material was evaluated by comparing with commercial NaYF₄:Er³⁺, Yb³⁺ phosphor, and our sample showed a high luminescence efficiency and good color performance, implying potential applications in a variety of fields.     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808 nm

As alternatives to Yb³⁺-sensitized up-conversion (UC) materials excited at 980 nm, Nd³⁺-sensitized UC phosphors irradiated by 808 nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from ⁵F₅→⁵I₈ and ⁵F₄/⁵S₂→⁵I₈ transitions of Ho³⁺ appeared in Nd³⁺/Yb³⁺/Ho³⁺ tri-doped NaLa(MoO₄)₂ through successive energy transfer Nd³⁺→Yb³⁺→Ho³⁺ under 808 nm excitation, in which Yb³⁺ ions were proven to be the energy transfer bridge between Nd³⁺ and Ho³⁺ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb³⁺, pulse width of the excitation laser and the addition of Ce³⁺ ion, which depends on the different population pathways to the green and red emitting states of Ho³⁺. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.     

Photoluminescent properties and site occupation preference in Bi3+, Eu3+ doped CaY4(SiO4)3O phosphor

Bi³⁺, Eu³⁺ doped CaY₄(SiO₄)₃O phosphors were synthesized through high temperature solid state reaction. Their photoluminescent properties were investigated and site occupation preference of Bi³⁺ in cationic sites was analyzed. The structure of CaY₄(SiO₄)₃O is characterized by three non-equivalent cationic sites with different coordination and cation-oxygen distances. By means of dielectric theory of the chemical bond for complex crystals, several kinds of chemical bond parameters like fractional covalence of CaY₄(SiO₄)₃O were calculated and integrated to yield environmental factor h_e. According to quantitative equations between the transition energy of Bi³⁺ and environmental factor h_e, the excitation bands at 308 and 226 nm were assigned to ¹S₀→³P₁ transition of Bi³⁺ in Y(6h) and Y(4f) site, respectively. Another excitation band centered at 210 nm should be the overlap of Bi³⁺ A-band in Ca site and C-band in Y(6h) site. Optical band gap of pure CYSO was calculated using Kubelka–Munk method from diffuse reflectance spectra. Red emission can be realized in CaY₄(SiO₄)₃O:Bi³⁺, Eu³⁺ under UV light excitation because of efficient energy transfer from Bi³⁺ to Eu³⁺ and decay behaviors of Bi³⁺ and Eu³⁺ emission were investigated. Without optimization, the internal quantum efficiency of CYSO:2%Bi³⁺, 7%Eu³⁺ at 310 and 393 nm excitations were 31.563%, 74.252%, respectively.     

Color-tunable up-conversion emission from Yb3+/Er3+/Tm3+/Ho3+ codoped KY(MoO4)2 microcrystals based on energy transfer

Tunable up-conversion luminescent material KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) has been synthesized by a typical hydrothermal process. Under 980 nm laser diode (LD) excitation, the emission intensity and the corresponding luminescence colors of KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) have been investigated in detail. The energy transfer from the Yb³⁺ sensitizer to Ho³⁺, Er³⁺ and Tm³⁺ activators plays an important role in the development of color-tunable single- phased phosphors. The emission intensity keep balance through control of the Ho³⁺ co-doping concentrations, white light was experimentally shown at KY(MoO₄)₂: 20 mol% Yb³⁺, 0.8 mol% Er³⁺, 0.5 mol% Tm³⁺, 1.0 mol% Ho³⁺ phosphor with further calcination at 800 °C for 4 h under 980 nm laser excitation. The color tunability, high quality of white light and high intensity of the emitted signal make these up-conversion (UC) phosphors excellent candidates for applications in solid-state lighting.     

Efficient near-infrared to visible and ultraviolet upconversion in polycrystalline BiOCl:Er3+/Yb3+ synthesized at low temperature

Er³⁺/Yb³⁺ co-doped BiOCl poly-crystals were synthesized by the conventional solid state method at 500 °C, which exhibited good crystalline and low phonon energy. Under 980 nm excitation, the samples showed intense red upconversion (UC) luminescence (Er³⁺: ⁴F_9/2→⁴I_15/2) as well as other four UC emission bands, including ultraviolet (UV) emission at 380 nm, violet emission at 411 nm, green UC emissions at 525 and 545 nm and near-infrared (NIR) emission between 800 and 850 nm, corresponding to the transitions of ⁴G_11/2, ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴I_9/2→⁴I_15/2 of Er³⁺, respectively. Interestingly, including the violet and green UC emissions, the red one originated a nearly three-photon process in this system, and a possible UC mechanism was proposed for the enhanced red emission.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Electrical properties and light up conversion effects in Bi3.79Er0.03Yb0.18Ti3−xWxO12 ferroelectric ceramics

Modified ceramic compositions of Bi_3.79Er_0.03Yb_0.18Ti_3−xW_xO₁₂ with fixed Er and Yb content, and a varying W content (x=0.0, 0.01, 0.03, 0.06 and 0.10) are prepared. The site selectivity of Er³⁺, Yb³⁺, and W⁶⁺ cations is analyzed, and their influence on the electrical and light up conversion properties is studied. Formation of single phase orthorhombic structure is confirmed with enhanced grain growth up to x=0.03, and for (x≥0.04–0.10) the grain growth is inhibited, and the orthorhombic distortion is relaxed. Raman spectroscopy reveals W⁶⁺ cation substitutes preferentially at the B-site replacing Ti⁴⁺ ions in the Bi₄Ti₃O₁₂ lattice structure. Increasing W⁶⁺ donor concentration reduces the conductivity effects by lowering the oxygen vacancies. Reduced dielectric losses (tan δ=0.003) and dispersion with frequency in the range (10⁻²–10 Hz) are observed, and improvements in the remnant polarization (2P_r=28.86 μC/cm²) are seen up to an optimum content of x=0.03. At higher W content (x>0.03), the properties tend to degrade due to structural relaxation and microstructural changes. Up conversion photoluminescence (UC-PL) under 980 nm excitation shows strong emission in the green and red bands due to enhanced crystal field around the Er³⁺ ions for an optimum W content of x=0.06. A weak blue emission band around (~492 nm) is observed by cooperative emission (CE) due to radiative relaxation of an excited Yb–Yb pair from a virtual level. Variation of UC emission intensity with pump-power confirms a two-photon mechanism for the up conversion process.     

White light emitting from YVO4/Y2O3:Eu3+,Bi3+ composite phosphors for UV light-emitting diodes

A series of (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 (0≤x≤0.54) composite phosphors was synthesized in one step by high temperature solid state reaction and the photoluminescence properties were investigated. By means of co-doping Eu³⁺ and Bi³⁺ ions into the composite matrices composed of YVO₄ and Y₂O₃ crystals, the YVO₄/Y₂O₃:Eu³⁺,Bi³⁺ phosphor exhibits simultaneously the blue (418 nm), green (540 nm) and orange-red (595, 620 nm) emissions. The broad blue and green emissions are attributed to the ³P₁–¹S₀ transitions of Bi³⁺ ion both in Y₂O₃ and in YVO₄ matrices. Moreover, the sharp orange-red emissions are attributed to the ⁵D₀–⁷F_1,2 transitions of Eu³⁺ ion in YVO₄ matrix. By tuning the mole ratio of YVO₄/Y₂O₃ matrices the white light-emitting could be obtained. The results indicated that when the mole ratio of Y₂O₃ (x) is at 0.11–0.54 mol, the (1−x)YVO₄/xY₂O₃:Eu³⁺_0.006,Bi³⁺_0.006 phosphors emit white light by combining the blue, green and orange-red emissions under the excitation of 360–370 nm wavelength which matches the emission of the commercial UV-LED diode. This implies that the phosphors may be the promising white light materials with broad absorption band for white light-emitting diodes.     

Triple NIR light excited up-conversion luminescence in lanthanide-doped BaTiO3 phosphors for anti-counterfeiting

Up-conversion luminescent (UCL) materials are excellent candidate for optical anti-counterfeiting and the exploitation of multi-wavelength NIR light triggered UC phosphors with tunable color emission is essential for reliable anti-counterfeiting technology. Herein, a series of lanthanide ions (Er³⁺, Er³⁺–Ho³⁺, and Yb³⁺–Tm³⁺) doped BaTiO₃ submicrometer particles are synthesized through a modified hydrothermal procedure. XRD and SEM measurements were carried out to identify the structure and morphology of the samples and their UCL properties under 808, 980, and 1550 nm NIR excitation are investigated. Er³⁺ singly doped sample exhibits Er³⁺ concentration-dependent and excitation wavelength-dependent emission color from green to yellow and orange. The corresponding UC mechanisms under three NIR light excitation are clarified. Pure red emission under 1550-nm excitation was obtained by introducing small amount of Ho³⁺ and the fluorescent lifetime test was used to confirm the energy transfer from Er³⁺ to Ho³⁺. In addition, Yb³⁺–Tm³⁺ co-doped sample shows intense blue emission from ¹G₄ → ³H₆ transition of Tm³⁺ under 980-nm excitation. As a proof of concept, the designed pattern using phosphors with red, green, and blue three primary color emissions under 1550, 808, and 980 nm NIR excitation was displayed to demonstrate their anti-counterfeiting application.     

Visible green upconversion luminescence of Er3+/Yb3+/Li+ co-doped CaWO4 particles

The upconversion (UC) luminescence of Li⁺/Er³⁺/Yb³⁺ co-doped CaWO₄ phosphors is investigated in detail. Single crystallized CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor can be obtained, co-doped up to 25.0/5.0/20.0 mol% (Li⁺/Er³⁺/Yb³⁺) by solid-state reaction. Under 980 nm excitation, CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor exhibited strong green UC emissions visible to the naked eye at 530 and 550 nm induced by the intra-4f transitions of Er³⁺ (²H_11/2,⁴S_3/2→⁴I_15/2). The optimum doping concentrations of Yb³⁺/Li⁺ for the highest UC luminescence were verified to be 10/15 mol%, and a possible UC mechanism that depends on the pumping power is discussed in detail.     

Efficient sensitization of Tb3+ emission by Dy3+ in CaMoO4 phosphors: Energy transfer,tunable emission and optical thermometry

Dy³⁺/Tb³⁺ codoped CaMoO₄ phosphors were synthesized by a simple sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The energy transfer process of Dy³⁺→Tb³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results verified that the efficient emission of Tb³⁺ was sensitized by Dy³⁺ under the excitation of 354 nm, realizing tunable emission in CaMoO₄ phosphors. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺: ⁵D₄→⁷F₅ (~546 nm) and Dy³⁺: ⁴F_9/2→⁶H_13/2 (~575 nm). It is expected that the investigated CaMoO₄ nanograins doped with Dy³⁺/Tb³⁺ have prospective applications in display technology and optical thermometry.     

Warm white-light generation in Ca9MgNa(PO4)7:Sr2+, Mn2+, Ln (Ln=Eu2+, Yb3+, Er3+, Ho3+, and Tm3+) under near-ultraviolet and near-infrared excitation

To obtain warm white-light emission, a series of Ca₉MgNa(PO₄)₇:Sr²⁺, Mn²⁺, Ln (Ln=Eu²⁺, Yb³⁺, Er³⁺, Ho³⁺, and Tm³⁺) phosphors were designed and their photoluminescence properties under near-ultraviolet and near-infrared excitation were studied. For near-ultraviolet excitation, blue-white emission is produced initially in the Eu²⁺ single-doped Ca₉MgNa(PO₄)₇, whose excitation band can well match with the near ultraviolet LED chip. By introducing Sr²⁺ ions into Ca₉MgNa(PO₄)₇:Eu²⁺, the Eu²⁺ emission band beyond 500 nm is enhanced obviously. Correspondingly, the emitting light color is tuned to nearly white. To generate warm white light further, Mn²⁺ is doped into the Ca_8.055MgNa(PO₄)₇:0.045Eu²⁺, 0.9Sr²⁺ and the correlated color temperature is decreased largely. For near-infrared excitation, the green, red, and blue emissions have been obtained in the Yb³⁺-Er³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Er³⁺ co-doped Ca₉MgNa(PO₄)₇ phosphors, respectively. And warm white light is also produced in the Ca₉MgNa(PO₄)₇:Yb³⁺, Er³⁺, Ho³⁺, Tm³⁺ under 980 nm excitation.     

Upconversion emission,cathodoluminescence and temperature sensing behaviors of Yb3+ ions sensitized NaY(WO4)2:Er3+ phosphors

A series of Yb³⁺ ions sensitized NaY(WO₄)₂:Er³⁺ phosphors were synthesized through a solid-sate reaction method. The X-ray diffraction (XRD), upconversion (UC) emission and cathodoluminescence (CL) measurments were applied to characterize the as-prepared samples. Under the excitation of 980 nm light, bright green UC emissions corresponding to (²H_11/2,⁴S_3/2)→⁴I_15/2 transitions of Er³⁺ ions were observed and the UC emission intensities showed an upward trend with increasing the Yb³⁺ ion concentration, achieving its optimum value at 25 mol%. Furthermore, the temperature sensing behavior based on the thermally coupled levels (²H_11/2,⁴S_3/2) of Er³⁺ ions was analyzed by a fluorescence intensity ratio technique. It was found that the obtained samples can be operated in a wide temperature range of 133–773 K with a maximum sensitivity of approximately 0.0112 K⁻¹ at 515 K. Ultimately, strong CL properties were observed in NaY(WO₄)₂:0.01Er³⁺/0.25Yb³⁺ phosphors and the CL emission intensity increased gradually with the increment of accelerating voltage and filament current.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Y(PO4)3 red phosphors

A series of red-emitting phosphors Eu³⁺-doped Sr₃Y(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Y(PO₄)₃:Eu³⁺ phosphors exhibit peaks associated with the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The integral intensity of the emission spectra of Sr₃Y_0.94(PO₄)₃:0.06Eu³⁺ phosphors excited at 392 nm is about 3.4 times higher than that of Y₂O₃:Eu³⁺ commercial red phosphor. The Commission Internationale de l’Eclairage chromaticity coordinates, the quantum efficiencies and decay times of the phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Y(PO₄)₃ phosphors are promising red-emitting phosphors pumped by near-UV light.