[Preparation and luminescence characteristics of white-light emitting Ca9.95-xNa0.75K0.25(PO4)7: Eu0.05(2+), Mn(x)2+ phosphors].

The Ca9.95-x Na0.75 K0.25 (PO4)7: Eu.0.05(2+), Mn(x)2+ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7) phosphors were synthesized by high temperature solid-state reaction, and their phase composition and fluorescence emission properties were studied. Due to the existence of double phases with similar crystal structure, the 5d-4f transition of Eu2+ ions in the phosphors emits a fluorescence of wide wavelength with peaks located at 491 nm and 540 nm respectively. The energy transfer between Eu2+ and Mn2+, together with the occupation of Mn2+ ions at the eight coordination sites in the phosphors, makes the 4T1 (4G)-6A1 (6S) transition of Mn2+ ions eimit red emission peaked at 635 nm. The combination of fluorescence emtted by Mn2+ and Eu2+ ions results in the emission of white light with color coordinates (0.3335, 0.2924), (0.3999, 0.3179) and (0.3307, 0.2564). The nearly pure white light emitting makes the phosphors show great application potential in the white light-emitting LEDs.

[Preparation and luminescence characteristics of Ba1.97 Ca1-x (B3O6)2: Eu(0.03)2+, Mn(x)2+ phosphor for white LED].

The Ba1.97 Ca1-x (B3O6)2 : Eu2+, Mn(x)2+ (x = 0, 0.03, 0.06, 0.15) phosphors were synthesized by high temperature solid-state reaction, and their phase composition and luminescence properties were studied. In these phosphors, Eu2+ locates at the crystal sites of Ba2+ and Ca2+ ions. Under 317 nm UV light excitation, the 5d --> 4f transition of Eu2+ forms a broad blue emission band with a peak at 450 nm. With the energy transfer from Eu2+ ions, Mn2+ ions emit a broad red band with the peak at 600 nm. The mixture of the broad blue emission and a broad red emission forms an approximate white light with the CIE chromaticity (x = 0.371, y = 0.282). The phosphors can be excited effectively by UV light in the range of 250-400 nm, so they are the potential candidates for single white light-emitting phosphor excited by UV-LED.

Waterproof Narrow-Band Fluoride Red Phosphor K2TiF6:Mn4+ via Facile Superhydrophobic Surface Modification.

With unique and efficient narrow-band red emission and broadband blue light absorption characteristics, Mn4+-activated fluoride red phosphors have gained increasing attention in warm white LEDs (WLEDs) and liquid crystal display (LCD) backlighting applications, whereas the intrinsic hygroscopic nature of these phosphors have inevitably limited their practical applications. Herein, a waterproof narrow-band fluoride phosphor K2TiF6:Mn4+ (KTF) has been demonstrated via a facile superhydrophobic surface-modification strategy. With the use of superhydrophobic surface modification with octadecyltrimethoxysilane (ODTMS) on KTF surfaces, the moisture-resistance performance and thermal stability of the phosphor KTF can be significantly improved. Meanwhile, the absorption, and quantum efficiency did not show obvious changes. The surface-modification processes and mechanism, as well as moisture-resistance performances and luminescence properties, of the phosphors have been carefully investigated. It was found that the luminous efficiency (LE) of the modified KTF was maintained at 83.9% or 84.3% after being dispersed in water for 2 h or aged at high temperature (85 °C) and high humidity (85%) atmosphere (HTHH) for 240 h, respectively. The WLEDs fabricated with modified KTF phosphor showed excellent color rendition with lower color temperature (2736 K), higher color rendering index (CRI, Ra = 87.3, R9 = 80.6), and high luminous efficiency (LE = 100.6 lm/W) at 300 mA. These results indicate that hydrophobic silane coupling agent (SCA) surface modification was a promising strategy for enhancing moisture resistance of humidity-sensitive phosphors, exhibiting great potential for practical applications.

Transition Metal-Involved Photon Upconversion.

Upconversion (UC) luminescence of lanthanide ions (Ln3+) has been extensively investigated for several decades and is a constant research hotspot owing to its fundamental significance and widespread applications. In contrast to the multiple and fixed UC emissions of Ln3+, transition metal (TM) ions, e.g., Mn2+, usually possess a single broadband emission due to its 3d5 electronic configuration. Wavelength-tuneable single UC emission can be achieved in some TM ion-activated systems ascribed to the susceptibility of d electrons to the chemical environment, which is appealing in molecular sensing and lighting. Moreover, the UC emissions of Ln3+ can be modulated by TM ions (specifically d-block element ions with unfilled d orbitals), which benefits from the specific metastable energy levels of Ln3+ owing to the well-shielded 4f electrons and tuneable energy levels of the TM ions. The electric versatility of d0 ion-containing hosts (d0 normally viewed as charged anion groups, such as MoO66- and TiO44-) may also have a strong influence on the electric dipole transition of Ln3+, resulting in multifunctional properties of modulated UC emission and electrical behaviour, such as ferroelectricity and oxide-ion conductivity. This review focuses on recent advances in the room temperature (RT) UC of TM ions, the UC of Ln3+ tuned by TM or d0 ions, and the UC of d0 ion-centred groups, as well as their potential applications in bioimaging, solar cells and multifunctional devices.