White light-emitting diodes (WLEDs) with high luminous brightness, low energy consumption, long lifetime and environmental friendliness can be applied in various fields. In order to improve the quality of white light, red phosphors are necessary.

The simplest and the most efficient deep-red to near-infrared-emitting emitters afford a new record external quantum efficiency for iridium(iii) complex based deep-red to near-infrared organic light-emitting diodes.

The application of white LEDs is hindered by the low efficiency of commercial red phosphors. Here, a novel narrow-line red phosphor is produced by a terbium chain in the form of Ce(3+)-(Tb(3+))n-Eu(3+) in the Na2Y2B2O7 host and is characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence lifetime, and the energy transfer (ET) processes between rare-earth ions in the host are discussed. The formation of terbium chain with a quite low content of Tb(3+) in Na2Y2B2O7 is realized by the ET processes of Ce(3+)-Tb(3+) and Tb(3+)-Eu(3+), and a new concept of saturation distance is put forward as an explanation for the first time. An energy level diagram is proposed to explain the ET processes in the phosphor of Na2Y2B2O7:Ce(3+),Tb(3+),Eu(3+). The emitting colour of the phosphor can be tuned from blue to green or yellow and finally to the orange-red region with increasing the content of Tb(3+). The quantum efficiency of the phosphor with an optimized ratio of rare-earth ions, Na2Y2B2O7:0.5% Ce(3+),60% Tb(3+),0.5% Eu(3+), is up to 77% under the excitation of 365 nm, which indicates that the as-synthesized phosphor is applicable to near-UV white LEDs.

The minimization of thermal quenching, which leads to luminescence loss at high temperatures, is one of the most important issues for near-infrared phosphors. In the present work, we investigated the properties of near-infrared Ca(Sc,Mg)(Al, Si)O 6 : Cr 3 + phosphors with a pyroxene-type structure under blue light excitation. The CaScAlSiO 6 : Cr 3 + end member of Ca-(Sc,Mg)(Al,Si)O 6 : Cr 3 + phosphor led to broadband emission at a full-width half maximum of 215 nm, whereas the CaMgSi 2 O 6 : Cr 3 + end member exhibited high thermal stability at 150 °C, with an intensity of 88.4 % of that at room temperature. The structural analysis and density functional theory calculations revealed the absence of soft conformations and local space confinement contributed to the high structural rigidity and weakened the thermal quenching effect.

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