Luminescence and Energy Transfer of Color-Tunable Y2Mg2Al2Si2O12:Eu2+,Ce3+ Phosphors

Multi-Band Emission of Pr3+-Doped Ca3Al2O6 and the Effects of Charge Compensator Ions on Luminescence Properties

Multi-band emission luminescence materials are of great significance owing to their extensive application in diverse fields. In this research, we successfully prepared a series of Pr3+-doped Ca3Al2O6 multi-band emission phosphors via a high-temperature solid-state method. The phase structure, morphology, luminescence spectra and decay curves were investigated in detail. The Ca3Al2O6:Pr3+ phosphors can absorb blue lights and emit lights in the 450-750 nm region, and typical emission bands are located at 488 nm (blue), 525-550 nm (green), 611-614 nm (red), 648 nm (red) and 733 nm (deep red). The influence of the Pr3+ doping concentration was discussed, and the optimal Pr3+ doping concentration was determined. The impacts of charge compensator ions (Li+, Na+, and K+) on the luminescence of Pr3+ were also investigated, and it was found that all the charge compensator ions contributed positively to the emission intensity. More importantly, the emission intensity of the as-prepared phosphors at 423 K can still maintain 65-70% of that at room temperature, and the potential application for pc-LED was investigated. The interesting results indicate that the prepared phosphors may serve multifunctional and advanced applications.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED's and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303-483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED's and photodynamic therapy for the cancer treatment.

Color-tunable emissions realized by Tb3+ to Eu3+ energy transfer in ZnGdB5O10 under near-UV excitation

Photoluminescent (PL) energy transfer (ET) between two typical rare earth activators Tb3+ and Eu3+ is utilized to achieve color-tunable emission and the color range is apparently dependent on the ET efficiency. In the target host ZnGdB5O10 (ZGBO), the relatively low symmetric coordination environment of the rare earth cation not only suppresses the parity-forbidden law of the 4f-4f transitions of Tb3+ in the near-UV region, but also enhances the internal quantum efficiency (IQE), where the optimal IQE is 65.61% for ZGBO:0.8Tb3+. Moreover, its ET to Eu3+ is highly efficient, i.e. 94.71% in ZGBO:0.8Tb3+,0.10Eu3+, which eventually leads to a wide range of color-tunable emissions from green (0.2915, 0.5915) to red (0.6207, 0.3731). The systematic PL spectral study on Tb3+/Eu3+ singly doped and co-doped phosphors suggests that the ET mechanism takes place through the electric dipole-dipole interaction according to the Inokuti-Hirayama (I-H) model. Additionally, the in situ high temperature PL spectra indicate the very high thermal stability of ZnGd0.19Tb0.8Eu0.01B5O10, indicating that it can be a potential candidate for near-UV light emitting diode-pumped phosphors.

Recent Advances in Multi-Site Luminescent Materials: Design, Identification and Regulation

The development of novel phosphor materials with excellent performance and modification of their photoluminescence to meet the higher requirements for applications are the essential research subjects for luminescent materials. Multi-site luminescent materials with crystallographic sites for the activator ions that broaden the tunable range of luminescent spectra and even enhance the luminescent performance have attracted significant attention in the pursuit of high-quality luminescence for white light-emitting diodes. Here, we summarize multi-site luminescence characteristics based on the different kinds of host and activator ions, introduce the identifications of multi-site activator ions via optical analysis, provide a structural analysis and theoretical calculation methods, and introduce the regulation strategies and advance applications of multi-site phosphors. The review reveals the relationship between crystal structure and luminescent properties and discusses future opportunities for multi-site phosphors. This will provide guidance for the design and development of luminescent materials or other materials science.

Designing bifunctional platforms for LED devices and luminescence lifetime thermometers: a case of non-rare-earth Mn4+ doped tantalate phosphors

Non-rare-earth Mn⁴⁺ doped tantalate (Sr₂GdTaO₆) phosphors exhibiting deep-red emission were synthesized. Afterward, the phase structure, morphology, and optical properties (e.g., emission spectra, concentration quenching, decay curves, thermal stability, quantum yields, etc.) were systematically investigated. Under the optimal conditions, the Sr₂GdTaO₆:0.005Mn⁴⁺ phosphor showed an excellent color purity of 96.41% while the chromaticity coordinates were (0.721, 0.279). Besides, the optimal sample exhibited good thermal stability, and, hence, it can be packaged into light-emitting diode (LED) devices. Red-emitting LED devices could show strong far-red emission and could be suggested for plant cultivation lighting. On the other hand, white-emitting LED devices could find use in indoor illumination. Moreover, with the aid of temperature-dependent lifetime (TDL), a good relative sensing sensitivity (1.73% K^-1 at 453 K) of the luminescent thermometer was established. Herein, all the above findings suggested that Sr₂GdTaO₆:Mn⁴⁺ phosphors are a potential candidate for bifunctional platforms of solid-state lighting and luminescence lifetime thermometers.

Bi3+ photoluminescence in Y1-xBixCa3(GaO)3(BO3)4 and energy transfer to Eu3+ and Tb3+ in co-doped phosphors

Bi³⁺ possesses outer shell lone pair electrons, and, thus the so-involved photoluminescence (PL) is sensitive to the surrounding coordination. Besides, the similarity in the structural chemistry between Bi³⁺ and rare earth (RE) ions inspires us to investigate the Bi³⁺-PL performance in RE³⁺-containing hosts. Herein, Y_1-xBi_xCa₃(GaO)₃(BO₃)₄ (0.01 ≤ x ≤ 0.15) compounds were prepared by a high temperature solid state reaction method. The successful cationic doping and phase purity were confirmed by powder X-ray diffraction analysis. This series of phosphors exhibit the very strong absorption of Bi^{3+ 1}S₀ → ³P₁ at 272 nm along with the intense blue emission with a maximum at 399 nm and a full width at half maximum (FWHM) of 59 nm. They retained 78.86% of the emission intensity at 150 °C, with reference to that at room temperature. Moreover, Bi³⁺ could also behave as a sensitizer to enhance the emission efficiency of RE³⁺ and thus to realize color-tunable phosphors. The energy transfer was proved in the co-doped phosphors Y_0.95-yBi_0.05Eu_yCa₃(GaO)₃(BO₃)₄ (0.05 ≤ y ≤ 0.6) and Y_0.95-zBi_0.05Tb_zCa₃(GaO)₃(BO₃)₄ (0.05 ≤ z ≤ 0.6), and color-tunable emissions from blue to red, or from blue to green were realized in these two series of phosphors.