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.

Synthesis, structure, and luminescence properties of Europium/Cerium/Terbium doped strontium-anorthite-type green phosphor for solid state lighting

Novel phosphor exploration and luminescence property regulation are two important strategies in pursing high performance phosphors for white light emitting diodes, and have attracted great attention from the researchers. Herein, novel green phosphors Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺,Tb³⁺ had been obtained by high-temperature solid-state reactions and their luminescence properties had been investigated in detail. Powder X-ray diffraction and Rietveld structure refinement results verified the phase purity and gave the crystal structure of the prepared samples. Due to the electric dipole transition between inter configurations of 4f^N and 4f^N-15d¹, Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺ exhibited intense broad excitation and emission bands, giving out green and blue emitting light under UV excitation, respectively. By codoping Tb³⁺ with Ce³⁺ in the host and utilizing the energy transfer, tunable blue to green emission had been obtained. The energy transfer mechanism had been determined to be electric dipole-quadrupole interaction through dynamic luminescence analysis using I-H model. The prepared phosphors exhibited good thermal stability with integral emission intensity at 150 °C remaining more than 80 % of the emission intensity at 25 °C. Moreover, by coating Sr₂Ga₂SiO₇:Eu²⁺ and Sr₂Ga₂SiO₇:Ce³⁺,Tb³⁺ on UV chips, green LED devices had been obtained. The investigation results indicated that the Eu²⁺ singly doped and Ce³⁺-Tb³⁺ codoped Sr₂Ga₂SiO₇ might be potential UV excited green phosphors for solid state lighting.

Luminescence property improvement and controllable color regulation of a novel Bi3+ doped Ca2Ta2O7 green phosphor through charge compensation engineering and energy transfer

In pursuit of warm WLEDs, exploration of novel phosphors and regulation of the existing phosphors are the two approaches usually used in the luminescent material field. In this work, we prepared green Ca₂Ta₂O₇:Bi³⁺ phosphors firstly and investigated their properties in detail. The as-prepared Ca₂Ta₂O₇:Bi³⁺ exhibits intense green emission in the 450-580 nm range under UV excitation, which matches well with the UV chip and can efficiently avoid the re-absorption problem. The improvement in the emission intensity and thermal stability of the phosphor was achieved using different charge compensation methods including codoping alkali metal ions (Li⁺, Na⁺, and K⁺), creating a cation vacancy, and host co-substitution (Ca²⁺ + Ta⁵⁺ → Bi³⁺ + Si⁴⁺, Ca²⁺ + Ta⁵⁺ → Bi³⁺ + Ge⁴⁺). Through systematic research, the emission intensity at room temperature was improved 2.1 times and the thermal stability was improved 2.9 times at 200 °C. By coating the prepared green sample with other commercial phosphors on the UV chip, warm WLEDs with Ra being 91.1 and CCT being 3990 K were obtained. Moreover, taking the Bi³⁺ → Eu³⁺ energy transfer strategy, the emitting color of the phosphor was tuned and yellow emitting phosphor was obtained. Our study indicates that Bi³⁺ doped Ca₂Ta₂O₇ might be a potential UV excited green phosphor for WLEDs. The charge compensation methods and the Bi³⁺ → Eu³⁺ energy transfer approach are valuable ways to improve and adjust the luminescence properties, which can further derivate a series of novel phosphors for improving the quality of WLED devices.

Rare Self-Luminous Mixed-Valence Eu-MOF with a Self-Enhanced Characteristic as a Near-Infrared Fluorescent ECL Probe for Nondestructive Immunodetection

Steady and efficient sensitized emission of Eu²⁺ to Eu³⁺ can be achieved through a rare mixed-valence Eu-MOF (L₄Eu^III₂Eu^II). Compared with the sensitization of other substances, the similar ion radius and configuration of the extranuclear electron between Eu²⁺ and Eu³⁺ make sensitization easier and more efficient. The sensitization of Eu²⁺ to Eu³⁺ is of great assistance for the self-enhanced luminescence of L₄Eu^III₂Eu^II, the longer luminous time, and the more stable electrochemiluminescence (ECL) signal. Simultaneously, L₄Eu^III₂Eu^II possesses near-infrared (NIR) fluorescence of around 900 nm and a mighty self-luminous characteristic, which render it useful as a NIR fluorescent probe and as a luminophore to establish a NIR ECL biosensor. This NIR biosensor can greatly reduce the damage to the detected samples and even achieve a nondestructive test and improve the detection sensitivity by virtue of strong susceptibility and environmental suitability of NIR. In addition, the CeO₂@Co₃O₄ triple-shelled microspheres further enhanced the ECL intensity due to two redox pairs of Ce³⁺/Ce⁴⁺ and Co²⁺/Co³⁺. The NIR ECL biosensor based on these strategies owns an ultrasensitive detection ability of CYFRA 21-1 with a low limit of detection of 1.70 fg/mL and also provides a novel idea for the construction of a highly effective nondestructive immunodetection biosensor.

Luminescence properties and energy transfer of K3LuF6:Tb3+,Eu3+ multicolor phosphors with a cryolite structure

In recent years, compounds with a cryolite structure have become excellent hosts for luminescent materials. In this paper, Tb³⁺ doped and Tb³⁺/Eu³⁺ co-doped K₃LuF₆ phosphors were prepared via a high temperature solid phase sintering method. The XRD, SEM, as well as photoluminescence excitation (PLE) and emission (PL) spectra were measured to investigate the structure and luminescence properties of the as-prepared samples. In the Tb³⁺/Eu³⁺ co-doped K₃LuF₆ samples, both characteristic emission spectra of Tb³⁺ and Eu³⁺ could be observed and the emission color of the K₃LuF₆:0.12Tb³⁺,xEu³⁺ phosphors could be adjusted from green to yellowish pink and the corresponding CIE values could be regulated from (0.2781, 0.5407) in the green area to (0.4331, 0.3556) in the yellowish pink area by controlling the concentration ratio of Eu³⁺/Tb³⁺. In addition, the energy transfer mechanism in Tb³⁺/Eu³⁺ co-doped K₃LuF₆ was calculated to be a quadrupole–quadrupole interaction from Tb³⁺ to Eu³⁺ based on the Dexter's equation.

Single-phase multicolor phosphors with a cryolite structure were obtained via energy transfer from Tb³⁺ to Eu³⁺.