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With increasing interest in mixed-anionic hydrides, a number of interesting properties have been reported. Here, the structural and optical properties of (Eu2+-doped) MCaH3–MCaF3 (M = Rb, Cs) are investigated. For M = Rb, a complete hydride–fluoride solid solution series is found and for M = Cs, the known solid solution series (0 ≤ x ≤ 1.70) can be extended to x = 3. In case of Cs, a very bright luminescence emission is observed in Eu2+-doped samples, whereas the luminescence is fairly weak in Rb based compounds. With increasing hydride content, a shift of the emission color from cyan-green to red can be observed. In contrast to earlier reports for mixed fluoride–hydride host, the redshift is not a gradual shift of a single broad emission band, but the appearance of new narrow emission bands on the low energy side, which are assigned to the occupation of sites with higher hydride content. Consequently, this finding represents the first example in a mixed anionic hydride with a site-sensitive emission for sites with locally varying hydride content in the first coordination sphere and may serve as a general example for emission color tuning taking advantage of mixed-anionic compounds.

The covalent character of (oxy)nitrides has enabled tuning of emission color for new Eu2+- and Ce3+-doped phosphors and widespread implementation in white light LEDs. Mn2+-doped (oxy)nitrides form a relatively unexplored class of luminescent materials with great potential as orange to near infrared (NIR) phosphor in white light and NIR LEDs. Here we report deep red broad band emission around 700 nm for Mn2+ in Ca-α-SiAlON. The emission shows a complex and gradual temperature quenching behavior and an unexpectedly large blue shift of the band maximum from 740 nm at 75 K to 670 nm at 475 K. This peculiar luminescence behavior is explained by disorder in the local (N,O)7 polyhedral coordination of the Mn2+ ions resulting in a variation in emission maximum and quenching temperature for differently coordinated Mn2+ ions. Interestingly, the present results deviate from previous reports on narrow band orange emission from Mn2+ in Ca-α-SiAlON. Careful analysis reveals that the orange emission likely originates from an AlN:Mn2+ impurity phase. Sensitization of the Mn2+ emission by strongly absorbing Eu2+, Yb2+ and Ce3+ ions was observed but with low efficiency as energy transfer to Mn2+via exchange interaction is ineffective for the relatively large (>5 Å) nearest neighbor separation in Ca-α-SiAlON. The new insights on Mn2+ emission show that for efficient orange/red emission in (oxy)nitrides, a tetrahedral coordination is required for Mn2+ while deep red/NIR emission can be expected for higher coordination numbers but is prone to thermal quenching. Sensitization of the Mn2+ emission is efficient only for exchange interaction and requires short (

Recent research on white light LED (w-LED) phosphors has focused on narrow-band green and red luminescent materials to improve the efficacy of w-LEDs and to widen the color gamut of w-LED-based displays. Mn2+ is a promising emitter capable of narrow-band emission, either green or red, depending on the local coordination. However, the extremely low absorption coefficients for the spin- and parity-forbidden d-d transitions in Mn2+ form a serious drawback and require addition of a sensitizer ion such as Ce3+ or Eu2+, with strong absorption in the blue. The performance of the codoped phosphor then critically depends on efficient energy transfer. Despite extensive research, a clear understanding of the Eu2+→ Mn2+ and Ce3+→ Mn2+ transfer mechanism is lacking. Typically, Dexter exchange interaction or electric dipole-quadrupole coupling are considered. Here we investigate Eu2+→ Mn2+ energy transfer in Ba2MgSi2O7 and show that the most probable mechanism is exchange interaction with fast (nanoseconds) energy transfer from Eu2+ to nearest-neighbor Mn2+ and much slower (>100 ns) transfer to next-nearest neighbors, as expected for exchange interaction. We critically evaluate previous studies where the assignment of dipole-quadrupole interaction was erroneously based on CMn8/3 concentration dependence of energy transfer efficiencies. Preferential Eu2+-Mn2+ pair formation is suggested as a mechanism that enhances energy transfer efficiencies.

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The Eu2+-doped mixed alkaline metal strontium borohydride chlorides ASr(BH4)3–xClx (A = K, Rb, Cs) and Eu2+-doped strontium borohydride chloride Sr(BH4)2–xClx have been prepared by mechanochemical synthesis. Intense blue photoluminescence for Sr(BH4)2–xClx (λem= 457 nm) and cyan photoluminescence for the perovskite-type mixed alkaline metal strontium borohydride chlorides ASr(BH4)3–xClx (A = K, Rb, Cs) (λem = 490 nm) is already observable after short milling times. Temperature dependent luminescence measurements reveal an appreciable blue shift with increasing temperature for all ASr(BH4)3–xClx (A = K, Rb, Cs) until 500 K. This extremely large shift, caused by structural relaxation, as well as the vibrationally induced emission band broadening can serve as a sensitive response signal for temperature sensing, and this unique behavior has, to the best of our knowledge, not been reported in any Eu2+ doped phosphor so far. Additionally, bright luminescence, high quantum efficiencies, and very low thermal quenching of these Eu2+-doped borohydrides show that such host materials could serve in solid state lighting applications., This project has received funding from the European Union's Horizon 2020 FET Open programme under grant agreement No 801305 (NanoTBTech).