Novel Cyan-Green-Emitting Bi3+-Doped BaScO2F, R+ (R = Na, K, Rb) Perovskite Used for Achieving Full-Visible-Spectrum LED Lighting

A novel blue emitting phosphor Ca1-ySryScBO4:Bi3+ with zero-thermal quenching for multi-scenario application

In recent years, Bi3+ activated phosphors have received a lot of attention from researchers; however, the performance and application areas of phosphors are yet to be developed. In this work, a series of CaScBO4(CSBO):xBi3+ phosphors were successfully prepared using a high-temperature solid-state method. Under UV excitation, blue light emission was achieved at 430 nm with a quantum yield of 91%, and at 423 K, the emission intensity retained 82.8% of the original intensity at 298 K. By crystal field engineering, the substitution of Sr2+ at the Ca2+ site enhances the temperature stability of the material, and at 423 K, 473 K and 573 K, the samples maintain 104%, 103% and 85% of the emission intensity at room temperature, respectively. It indicates that the cation substitution causes the increase in the oxygen vacancy concentration, and the oxygen vacancy defect compensates the energy lost in electrons at high temperature, producing resistance to anti-TQ performance. Finally, a blue-violet LED was fabricated by using the phosphor and an ultraviolet LED chip, and white LEDs (CCT = 4683 K, Ra = 89.7) were obtained by co-packaging this phosphor with commercial phosphors and a UV chip. Importantly, the great potential of this phosphor in the field of plant lighting and biocontrol can be demonstrated.

Augmenting cyan emission in vanadate garnets via Dy3+activation for light emitting devices and multi-mode optical thermometry

Developing cyan-based phosphors is inevitable to bridge the cyan gap to generate white light with a high color rendering index. Herein, the blue-green emission from the VO43- center in the Sr2NaMg2V3O12 host is augmented via activating with Dy3+ ions. Dual emission from the Sr2NaMg2V3O12:Dy3+ system under 335 nm excitation is due to the energy transfer from VO43- to the Dy3+ center. An increase in the ratio of yellow to blue bands (Y/B) is noted with the increase in the concentration of Dy3+. Apart from the higher activation energy of 0.41 eV, excellent color stability with a small thermochromic shift is noted at elevated temperatures. The light emitting device fabricated based on the Sr2NaMg2V3O12:Dy3+ phosphor presents bright cyan emission with CIE coordinates of (0.250, 0.352), a CCT of 9826 K, and a CRI of 53 with stable emission even at higher input currents. The application of Sr2NaMg2V3O12:Dy3+ in multi-mode temperature sensing is also discussed. The maximum relative temperature sensitivity of 1.32, 0.41, and 1.9% K-1 at 380, 300, and 460 K is obtained for the fluorescence, fluorescence intensity ratio and excitation intensity ratio methods. Thus, the present work details the capability of Dy3+-based vanadate garnet phosphors for solid-state lighting and temperature sensing.

NUV-pumped red-emitting Ca9MnK(PO4)7 phosphor: energy transfer and charge compensation

The development of novel Mn-based phosphor hosts has received increasing interest in the search for highly efficient red emitting phosphors for white LED applications. In this study, Ca₉MnK(PO₄)₇, a compound with the β-Ca₃(PO₄)₂-type structure, was successfully synthesized by a high-temperature solid-state reaction process. The Eu²⁺-doped Ca₉MnK(PO₄)₇ phosphor exhibits a broadband red emission peaking at 650 nm. The optimal excitation wavelength is 395 nm, which matches that of commercial ultraviolet (NUV) chips. Codoping Ce³⁺ ions into the Ca₉MnK(PO₄)₇:Eu²⁺ phosphor efficiently improves Mn²⁺ luminescence. Here, Ce³⁺ acts as a charge compensator rather than a sensitizer and substantially increases the effective number of Eu²⁺ and finally improves the red emission of Mn²⁺. The charge compensation mechanism is also verified by codoping some optically inert rare earth ions (Ln³⁺) including Y³⁺, La³⁺ and Gd³⁺. The results demonstrate that these developed Ca₉MnK(PO₄)₇:Eu²⁺, Ln³⁺ phosphors have great potential for application in NUV-based white LEDs. The energy transfer approach combined with the charge compensation technique is valuable for improving the performance of the red-emitting Ca₉MnK(PO₄)₇:Eu²⁺ phosphor, which can further be used in developing other Mn-based phosphors.

Dazzling Red-Emitting Europium(III) Ion-Doped Ca2LaHf2Al3O12 Garnet-Type Phosphor Materials with Potential Application in Solid-State White Lighting

Bright red-emitting phosphors with high color purity and high photoluminescence quantum yield (PLQY) are highly demanded for the fabrication of high-performance warm-white light-emitting diodes (LEDs). Herein, we demonstrated a novel efficient Eu³⁺-activated Ca₂LaHf₂Al₃O₁₂ garnet phosphor with excellent luminescence properties for near-ultraviolet (near-UV) excited warm-white LEDs. The Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors exhibited an intense excitation spectrum in the near-UV region with a maximum around 394 nm, and they produced dazzling red luminescence peaking at 592, 614, 659, and 711 nm due to the ⁵D₀ → ⁷F_J (J = 1-4) transitions of Eu³⁺ ions when the excitation wavelength was set at 394 nm. Luminescent properties have been studied as a function of Eu³⁺ doping concentration, and the highest emission intensity was achieved at 50 mol % Eu³⁺, while the dipole-dipole interaction brought the concentration quenching effect. The Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ sample exhibited CIE chromaticity coordinates of (0.6419, 0.3575) with a color purity of 92.7%, and its PLQY was measured to be 64%. The thermal stability and activation energy of Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphors were also discussed and analyzed. Finally, we made a near-UV chip-based white LED device in which the Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺ phosphor was utilized as a red ingredient. A bright warm-white light emission was realized from this LED device under 80 mA driving current, accompanied by a high color rendering index (CRI) of 88.3, a low correlation color temperature of 3853 K, and good CIE chromaticity coordinates of (0.3909, 0.3934). These results revealed that these red-emitting Ca₂LaHf₂Al₃O₁₂:Eu³⁺ phosphors have promising application prospect in near-UV-excited warm-white LEDs with high a CRI.

Realization of an Optical Thermometer via Structural Confinement and Energy Transfer

The influence of temperature on a variety of physiological or chemical processes has generated considerable interest, and recently noninvasive lanthanide-incorporated optical thermometers have been considered as promising candidates for monitoring its changes at different scales. Herein, a novel Bi³⁺-activated Sr_3-xGd_xGaO_4+xF_1-x phosphor with tunable color has been constructed by a cooperative cation-anion substitution strategy with to the replacement of [Sr²⁺-F^-] by [Gd³⁺-O^2-]. When x = 0, the sample Sr₃GaO₄F/Bi³⁺ possesses a peak wavelength at 438 nm, and this value will shift to 470 nm if x is equal to 1 (Sr₂GdGaO₅/Bi³⁺). In addition, photoluminescence tuning from blue to red has been realized successfully by an efficient Bi³⁺ → Eu³⁺ energy migration model in Sr_2.6Gd_0.4GaO_4.4F_0.6 samples. The specific Bi³⁺ → Eu³⁺ energy transfer has been explained by dipole-dipole interactions derived from a model of the Dexter pathway. Intriguingly, the two dopants (a blue signal from Bi³⁺ and a red signal from Eu³⁺) possess different thermal responses to increasing temperature. Accordingly, the intensity ratio values are sensitive to the temperature changes. The energy level cross relaxation causes the quenching effect of Bi³⁺, and the multi-phonon de-excitation mode leads to the thermal quenching of Eu³⁺. At room temperature (298 K), the determined maximum relative sensitivity (S_r) is 1.27% K^-1. Moreover, the absolute sensitivity (S_a) is 0.067 K^-1 since the temperature is elevated to 523 K. The collected results are superior to most of the reported optical thermometry materials.