MBe₂₀N₁₄:Eu²⁺ (M = Sr, Ba): Highly Condensed Nitridoberyllates with Exceptional Highly Energetic Eu²⁺ Luminescence

Abstract

The isotypic nitridoberyllates MBe 20 N 14 with M = Sr, Eu, Ba have been synthesized at high temperatures under a N 2 atmosphere. The crystal structures were solved and refined from single-crystal X-ray diffraction data (I4/m (no. 87), Z = 2, SrBe 20 N 14 :Eu 2+ , a = 6.525(2), c = 12.133(4) Å; EuBe 20 N 14 , a = 6.5241(8), c = 12.136(2) Å; BaBe 20 N 14 :Eu 2+ , a = 6.540( 6), c = 12.214(11) Å). MBe 20 N 14 contains a rigid network of multiply edge-sharing BeN 4 tetrahedra with a degree of condensation (i.e., atomic ratio Be/N) κ = 1.43. Eu 2+ -doped samples of MBe 20 N 14 (M = Sr, Ba) show two emission bands in the blue-to-green spectral region: regular narrow-band blue Eu 2+ emission (λ em1 ≈ 426−428 nm, full width at half-maximum (fwhm) ≈ 22−25 nm/1180−1310 cm −1 ) and trapped exciton emission in the blue-green spectral region (λ em2 ≈ 530−540 nm, fwhm > 100 nm). MBe 20 N 14 show high chemical and thermal stability. For SrBe 20 N 14 , a wide band gap (E g = 4.6 eV) and a high Debye temperature (θ D = 1214 K) were calculated. Large band gaps, chemical and thermal stability, and rigid networks make nitridoberyllates a promising class of host compounds for narrow-band emitting light-emitting diode phosphors.

Nitridophosphate‐Based Ultra‐Narrow‐Band Blue‐Emitters: Luminescence Properties of AEP8N14:Eu2+ (AE=Ca, Sr, Ba)

“…Corresponding emission wavelengths ( λ em (CaP 8 N 14 :Eu 2+ )=470 nm; λ em (SrP 8 N 14 :Eu 2+ )=440 nm) are comparable with other alkaline earth nitridophosphates, for example, BaP 2 N 4 :Eu 2+ ( λ em =454 nm), despite the different coordination spheres of the activator ions (Table ). Considering the fwhm of 1380 cm −1 (31 nm) and 1350 cm −1 (26 nm), respectively, CaP 8 N 14 :Eu 2+ and SrP 8 N 14 :Eu 2+ can be classified as the first P/N‐based ultra‐narrow‐band blue emitters and can compete with related (oxo)nitridoberyllate and —silicate phosphors …”

“…Over the years, research on new phosphors expanded to a range of related compound classes, such as nitridoalumosilicates and nitridolithoaluminates, with Ca[AlSiN 3 ]:Eu 2+ and Sr[LiAl 3 N 4 ]:Eu 2+ showing highly efficient red emission . Recently, beryllium‐containing nitrides have been shown to feature extremely narrow‐band emissions in the blue to cyan spectral region …”

Ca[B8O11(OH)4] : Eu2+ – A Highly Efficient Deep Blue‐Emitting Phosphor Prepared by Low‐Temperature Self‐reduction

“…As shown in Figure 4a, both the minimum position of the conduction band and the maximum position of the valence band are located at the Gamma point, indicating that CBH is a direct band gap material. The calculated band gap of CBH is 7.48 eV, which is a necessary condition for achieving high PLQY phosphors [51,52] . The size of the band gap sets the relative position of the rare‐earth 5d orbitals with respect to the conduction band (CB) of the matrix crystal, which can influence the optical response.…”

Chasing Down the Eu2+ Ions: The Delicate Structure−Property Relationships in the Ultra‐Narrow Band Phosphor K1.6Na2.1Li0.3[Li3SiO4]4:Eu2+

“…[ 40 ] This wavelength range is of high interest for, for example, human‐centric lighting LEDs that affect the melatonin production within the body and thus have an influence on the circadian rhythm. One potential material class formally fulfilling the requirements for efficient cyan‐emitting phosphors are Eu 2+ ‐activated oxido(nitrido)beryllates AE Li 2 [Be 4 O 6 ] ( AE = Sr, Ba) and Sr[Be 6 ON 4 ], [ 46,47 ] or the highly condensed nitridoberyllates AE Be 20 N 14 ( AE = Sr, Ba) [ 48,49 ] but the Be‐related toxicity limits their application.…”