Journal of Luminescence最新文献

New single phase and adjustable emission phosphors have attracted a lot of attention because of the good luminous properties. In this work, Sm³⁺ doped CaTbAl₃O₇ phosphors are prepared in air by solid-state method. The crystal structure, concentration dependent spectra, lifetimes, and luminescence properties are investigated. Because of the 4f⁸ → 4f⁷5d¹ and 4f → 4f transitions of Tb³⁺ ion, host (CaTbAl₃O₇) shows an excitation spectrum in the range of 220–520 nm under monitored at 544 nm and emits yellow-green light under excitation 248, 284, and 368 nm due to the ⁵D₄ → ⁷F_J (J = 0, 1, 2, 3, 4, 5, and 6) transitions of Tb³⁺ ion. CaTbAl₃O₇:Sm³⁺ under monitored 598 nm contains the excitation spectral peaks of both CaTbAl₃O₇ and Sm³⁺ ion. With excitation at 368 nm, CaTbAl₃O₇:Sm³⁺ glows orange-red light, its PL spectrum has both host (CaTbAl₃O₇) and Sm³⁺ ion contributing, and the chromaticity coordinates are about (0.5499, 0.4351). Under excitation 402 nm, the red-orange emission of CaTbAl₃O₇:Sm³⁺ is only the contribution of Sm³⁺ ion and the chromaticity coordinates are about (0.5823, 0.4168). The energy transfer process from Tb³⁺ in host (CaTbAl₃O₇) to Sm³⁺ ions can be confirmed via the spectral properties. We explain the luminous mechanism of CaTbAl₃O₇:Sm³⁺ by the energy level diagrams of Tb³⁺ and Sm³⁺.

In this paper, a novel far-red emitting garnet-structured phosphor, Y₃Ga₃MgSiO₁₂:Mn⁴⁺, was synthesized using the traditional solid-state reaction method. The prepared Y₃Ga₃MgSiO₁₂:Mn⁴⁺ phosphor exhibits a broad excitation band in the range of 250–600 nm and emits bright far-red light in the wavelength range of 630–710 nm, with a peak at 670 nm when excited at 354 nm. The optimal doping concentration of Mn⁴⁺ is approximately x = 0.006. Beyond this concentration, luminescence quenching occurs due to energy transfer between Mn⁴⁺ ions caused by dipole-dipole interactions. The effect of cation substitution on the photoluminescence properties of Y₃Ga₃MgSi_(1-y)Ge_yO₁₂:0.01Mn⁴⁺ phosphors was studied, revealing that the substitution of Ge⁴⁺ ions can systematically influence the luminescence of Mn⁴⁺. The Y₃Ga₃MgSiO₁₂:0.01Mn⁴⁺ phosphor exhibits excellent color purity, and its emission spectrum matches well with the absorption spectra of photosensitive pigments P_R and P_FR. The temperature-dependent emission spectra of Y₃Ga₃MgSi_(1-y)Ge_yO₁₂:0.01Mn⁴⁺ phosphors were studied, and the activation energy was calculated. The substitution of Ge⁴⁺ ions can improve the thermal stability of the samples. These outstanding photoluminescence properties suggest that Y₃Ga₃MgSiO₁₂:Mn⁴⁺ phosphor has application potential in pc-WLEDs and indoor plant cultivation pc-RLEDs. The findings of this work provide ideas for the design of high performance Mn⁴⁺ activated phosphors.

Photon avalanche is a special phenomenon of upconversion that the luminescence emission intensity exhibits a significant nonlinear response to the excitation power. Traditional photon avalanche is typically observed in bulk materials, which is not enough to meet requirements of modern techniques as it expect smaller in size and stronger in signal response. In this study, photon avalanche effect is obtained from single LiYF₄: Yb³⁺/Pr³⁺ microparticle. The emission intensity demonstrates a 16-order nonlinear coefficient with excitation intensity change under 835 nm laser excitation. By utilizing the plasmonic effect of noble metal nanoparticles, we successfully modulate the photon avalanche of the particle. Obvious reduction in the threshold of photon avalanche is detected when plasmonic gold nanorods are assembled to the surface of LiYF₄: Yb³⁺/Pr³⁺ microparticle.

The exploration of efficient narrowband emission phosphors is crucial for white light-emitting diodes (WLEDs) in high-performance backlighting applications. Up to now, the discovery of narrow-band Bi³⁺-doped phosphors for emerging applications remains challenging because Bi³⁺ typically exhibits broadband emission properties. A novel narrow-band blue phosphor (Ca₄SnGe₃O₁₂:Bi³⁺) was successfully synthesized, benefiting from the highly symmetric crystal environment and tightly connected rigid structure of the garnet structure. The phosphor demonstrates broad excitation in the near-ultraviolet (n-UV) region and emits narrowband blue light at 442 nm (FWHM = 36 nm) with a color purity of 94.7 %. In this paper, the assignment of different luminescence centers and the use of Zr/Hf to partially replace Sn to enhance luminescence performance are studied. The reasons for the consequent changes in luminescence behavior are explained in detail. The use of narrowband commercial red K₂SiF₆:Mn⁴⁺, green β-Sialon:Eu²⁺, and synthetic blue luminescent materials as RGB emitters covered 81 % of the National Television System Committee (NTSC) color space, demonstrating great potential for liquid-crystal-display (LCD) backlight use.

Trivalent terbium ion doped lanthanum tungstate (La_2-xTb_x(WO₄)₃; x = 0.6,1.0,1.4) and terbium tungstate (Tb₂(WO₄)₃) phosphors were successfully synthesized via optimized microwave-assisted co-precipitation technique. The phase purity and crystallinity of the prepared samples were confirmed using the powder XRD technique. The photoluminescence studies revealed a quenching-free emission up to 70 % of Tb³⁺ doping concentration, even though the emission intensity slightly decreases under host excitation since it becomes less relevant at higher doping concentrations. The experimental and calculated oscillator strengths were evaluated using absorption data and further used to quantify the Judd - Ofelt (JO) intensity parameters, which appeared in a trend of Ω₂>Ω₄>Ω₆ for all samples. As a theoretical approach to assure the excellency of the tungstate host, the radiative parameters were calculated from the emission data using the JO analysis technique. The dominance in the values of stimulated emission cross section and gain bandwidth corresponding to ⁵D₄→⁷F₅ transition of Tb³⁺ ion of lanthanum tungstate proclaims it as an excellent green phosphor. Hence, the less susceptibility of the tungstate host towards concentration quenching is confirmed in the present work.

Pristine and europium doped calcium magnesium silicate (CMS and CMS: Eu³⁺) phosphor having akermanite (Ca₂MgSi₂O₇), monticellite (CaMgSiO₄) and merwinite (Ca₃MgSi₂O₈) phases are synthesized via solid state reaction method. The modification of photoluminescence properties such as emission intensity, decay time and quantum yield (QY) due to the variation of the crystal structure, local site symmetry and coordination geometry of akermanite, monticellite and merwinite phases are studied. The merwinite phase is optimized at an annealing temperature of 900 °C, whereas monticellite phase is at 1100 °C. The agglomerated morphology changes to particle formation as the annealing temperature changes from 900 °C to 1100 °C. The lattice parameters and site preference of Eu³⁺ ions are determined using Density Functional Theory (DFT) calculations. The analysis of lattice expansion, formation enthalpy (${\Delta H}_f$) and mixing energy (${\Delta H}_m$) reveal the preference of Eu³⁺ occupation in the Ca²⁺ cationic site over Mg²⁺ for all three phases. The blueshift and redshift of Mg-O and Ca-O stretching in the Fourier Transform Infra-Red (FTIR) analysis agree with the DFT calculation. UV–visible spectra analyses reveal a modification in optical bandgap with Eu³⁺ addition. The highest intensity ⁵D₀→⁷F₂ induced electric dipole (ED), hypersensitive transition indicates the preference of Eu³⁺ ions in a non-inversion center for all the phases. This agrees with the higher ${\Omega }_2$ values from Judd-Ofelt (J-O) parameter calculations and local site symmetry analysis of DFT-optimized structures. The monticellite phase exhibits maximum crystal field splitting due to its octahedral geometry, whereas the akermanite phase, with its distinct dodecahedral geometry, displays maximum emission intensity, an extended decay time, and the highest quantum yield (QY). The modification of photoluminescence properties of the three phases is analyzed in detail based on the coordination geometry and the distortion in local sites due to Eu³⁺ doping in the Ca and Mg sites. CIE color chromaticity analysis confirms the orange-red emission with 91.94 %, 90.88 % and 90.24 % color purity for akermanite, monticellite and merwinite phases respectively. Hence, the present study throws light on the potency of the akermanite phase of CMS: Eu³⁺ phosphor with 70 % QY as the optimal matrix for Eu³⁺ ions over monticellite and merwinite host matrices.

Heterostructures with thin GaSb layers embedded in a GaP matrix are studied by transmission electron microscopy as well as steady-state and transient photoluminescence. For a single, one monolayer thick deposition with subsequent overgrowth, nonmonotonic Sb segregation results in self-organized Ga(Sb,P) double-quantum well (QW) formation. One QW is positioned deep in GaP at the designated place according to the heterostructure design, and the other QW is in the near surface region after 40 monolayers of GaP overgrowth. Both QWs are characterized by an indirect band gap. The band alignment in the QWs is identified as type I. In spite of the long (up to milliseconds) exciton lifetimes in the QWs in combination with the electron g factor of +2, the emission of the QWs demonstrates a low circular polarization degree in longitudinal magnetic fields as strong as 10 T. We demonstrate that the electron spin polarization in the Ga(Sb,P)/GaP heterostructure subject to a magnetic field occurs in the GaP layer, and spin-polarized charge carriers captured in the QWs store their spin orientation up to the millisecond time range, indicating very long spin relaxation times for the strongly localized electrons in the Ga(Sb,P)/GaP QWs.

The transition metal Mn⁴⁺ activated phosphors have attracted increasing attention due to the potential uses in phosphor-converted lighting emitting diodes (LEDs). Herein, the far-red emitting SrLaMgTa_1-yAl_yO₆:Mn⁴⁺ (y = 0−0.15) oxide phosphors were successfully synthesized by the high-temperature solid state reaction, in which the Mn⁴⁺ acted as an activator. The monoclinic double perovskite crystal structure, chemical composition, and 4+ state of activator Mn were confirmed by means of X-ray diffraction Rietveld refinement, scanning electron microscopy elemental mapping, and X-ray photoelectron spectroscopy. The optical properties were characterized with photoluminescence excitation and emission spectra, temperature-dependent emission spectra, and electroluminescence spectra. The excitation spectra are interweaved with the ligand-to-metal charge transfer band of Mn−O and intrinsic transitions (⁴A_2g→⁴T_1g, ⁴A_2g→²T_2g, and ⁴A_2g→⁴T_2g) of Mn⁴⁺, locating at the ultraviolet and blue light region. The emission spectra mainly contain a dominant far-red emission band from 650 to 775 nm with peaks at 695 and 708 nm, which are ascribed to the ²E_g→⁴A_2g transition of Mn⁴⁺. Moreover, the cationic substitution strategy with tiny Al³⁺ occupying Ta⁵⁺ octahedral site, promotes the improvement of luminescence intensity and optical thermal stability. The quantum yield of optimal phosphor reaches 88.2 % and the fluorescence intensity at 373 K (100 °C) retains 83.4 % in respect to that at ambient temperature, implying the phosphor with intense and thermally stable luminescence. The phosphor is packaged with 365 nm chip to fabricate an LED device, and the electroluminescence result is quite consistent with the photoluminescence, matching well with the absorption spectrum of the phytochrome. The Mn⁴⁺ activated oxide phosphors with intense far-red emission are promising for plant cultivation lighting.

Phosphor-converted LEDs (pc-LEDs) emitting in the visible region based on undoped tellurate double perovskites have not been explored till now. A cyan-emitting pc-LED is fabricated using the host Ba₂MgTeO₆ double perovskite for the first time. The as-fabricated cyan LED emits light in the visible region with the maximum emission at 484 nm. The obtained CIE coordinates of (0.26, 0.37) ensure a cyan light, and LED exhibits superior color stability even at higher input drive current. An attempt to develop a white emitting phosphor was done by substituting Eu³⁺ ions into the Ba₂MgTeO₆ matrix. Followed by this, a phosphor converted LED emitting in the bluish white region was fabricated by combining near UV chip and BMTO: 0.02 Eu³⁺ phosphor. Further, an inherent near-infrared (NIR) luminescence in Ba₂MgTeO₆ is also discovered and it originates from the ³T_1u, ³A_1u – ¹A_1g electronic transitions within the Te⁴⁺ ions. Upon 367 nm excitation, Ba₂MgTeO₆ exhibits strong broadband NIR emission, which spans from 780 nm to 1150 nm with a maximum emission at 889 nm and full width at half maximum (FWHM) of about 115 nm. Finally, an efficient pc-LED emitting in the NIR region is fabricated using the intrinsic near-infrared luminescence observed in the Ba₂MgTeO₆ phosphor. The pc-LED covering the near infrared region can be potentially used for various applications, including plant cultivation, biosensors, night vision cameras, etc.