Controllable Eu2+-Doped Orthophosphate Blue-/Red-Emitting Phosphors: Charge Compensation and Lattice-Strain Control.

Cation-substitution-induced controllable luminescence tuning could efficiently optimize and improve the luminescence performances of novel phosphor materials for realizing high-quality lighting. As important members of the orthophosphate family, ABPO4 (A = alkali metal Li, Na, K, Rb, Cs; B = alkali earth metal Mg, Ca, Sr, Ba) offers an abundant cation lattice environment for rare earth ions. Herein, we successfully prepared a broad-band red-emitting CsMgPO4:Eu2+ phosphor with an emission peak at 628 nm (fwhm = 118 nm). A series of cation-substitution strategies are designed to adjust and enhance its luminescence performances. The corresponding mechanisms are also investigated and proposed reasonably. A charge-compensation strategy of [Eu2+-Si4+] → [Cs+-P5+] could dramatically enhance the quenching concentration from 0.04 to 0.30, which is attributed to the decrease of Eu3+. Two cation-substitution strategies of larger Ba2+ (Sr2+) ions for Mg2+ ions could achieve superior emission adjustment of Eu2+ ions from the red to blue (yellow) region due to local lattice distortion. Interestingly, a consecutive emission adjustment from the red to blue region by simply changing the annealed temperature is reported for the first time, and the possible emission tuning mechanism is revealed based on a local lattice-strain control. This study could serve as a guide in developing Eu2+-activated ABPO4 phosphors with improving luminescence performance and controllable luminescence adjustment based on charge compensation and lattice-strain control through various cation substitutions.

Bismuth activated full spectral double perovskite luminescence materials by excitation and valence control for future intelligent LED lighting.

A novel La2Mg1.14Zr0.86O6:Bi3+ double perovskite phosphor with excitation-induced blue/green photoluminescence tuning is reported. By designing Bi3+→ Eu3+ energy transfer, single-composition white light with wide-scale adjustable corrected color temperatures (CCTs) is successfully achieved. This work initiates a new insight to explore phosphors with excitation-induced photoluminescence tuning and wide CCT control for future intelligent LED lighting.

Strategies for Designing Antithermal-Quenching Red Phosphors.

Nowadays, red phosphor plays a key role in improving the lighting quality and color rendering index of phosphor-converted white light emitting diodes (w-LEDs). However, the development of thermally stable and highly efficient red phosphor is still a pivotal challenge. Herein, a new strategy to design antithermal-quenching red emission in Eu3+, Mn4+-codoped phosphors is proposed. The photoluminescence intensity of Mg3Y2(1- y )Ge3O12:yEu3+, Mn4+ (0 ≤ y ≤ 1) phosphors continuously enhances with rising temperature from 298 to 523 K based on Eu3+ → Mn4+ energy transfer. For Mg3Eu2Ge3O12:Mn4+ sample, the integrated intensity at 523 K remarkably reaches 120% of that at 298 K. Interestingly, through codoping Eu3+ and Mn4+ in Mg3Y2Ge3O12, the photoluminescence color is controllably tuned from orangish-red (610 nm) to deep-red (660 nm) light by changing Eu3+ concentration. The fabricated w-LEDs exhibit superior warm white light with low corrected color temperature (CCT = 4848 K) and high color rendering index (R a = 96.2), indicating the promising red component for w-LED applications. Based on the abnormal increase in antistokes peaks of Mn4+ with temperatures, Mg3Eu2Ge3O12:Mn4+ phosphor also presents a potential application in optical thermometry sensors. This work initiates a new insight to construct thermally stable and spectra-tunable red phosphors for various optical applications.

New strategy for designing orangish-red-emitting phosphor via oxygen-vacancy-induced electronic localization.

Phosphor-converted white-light-emitting diodes (pc-WLED) have been extensively employed as solid-state lighting sources, which have a very important role in people's daily lives. However, due to the scarcity of the red component, it is difficult to realize warm white light efficiently. Hence, red-emitting phosphors are urgently required for improving the illumination quality. In this work, we develop a novel orangish-red La4GeO8:Bi3+ phosphor, the emission peak of which is located at 600 nm under near-ultraviolet (n-UV) light excitation. The full width at half maximum (fwhm) is 103 nm, the internal quantum efficiency (IQE) exceeds 88%, and the external quantum efficiency (EQE) is 69%. According to Rietveld refinement analysis and density functional theory (DFT) calculations, Bi3+ ions randomly occupy all La sites in orthorhombic La4GeO8. Importantly, the oxygen-vacancy-induced electronic localization around the Bi3+ ions is the main reason for the highly efficient orangish-red luminescence. These results provide a new perspective and insight from the local electron structure for designing inorganic phosphor materials that realize the unique luminescence performance of Bi3+ ions.