Cr³⁺ Activated Garnet Phosphor with Efficient Blue to Far‐Red Conversion for pc‐LED

Abstract

Far‐red (FR) phosphor‐converted light‐emitting diodes (pc‐LEDs) driven by blue LED chips are novel light sources for applications in phototherapy, photosynthesis, natural light simulation, and so on but still bear low electricity‐to‐FR light conversion efficiency (≤ 23%) due to deficiency of phosphors that have both high blue light absorptance and high FR internal quantum efficiency (IQE) for the realization of efficient blue to FR conversion. FR Ca3Sc2Si3O12 (CSSG):Cr3+ garnet phosphor has ultra‐high IQE (> 90%) but low blue light absorption. Here, a twofold increase of blue light absorption cross‐section is reported with still high FR IQE via Lu3+−Mg2+ substitution for Ca2+−Sc3+ in CSSG:Cr3+ to form Ca3–xLuxMgxSc2–xSi3O12:Cr3+ garnet solid solution, which is attributed to enhanced mixing of odd‐parity configuration into 3d configuration of Cr3+ induced by the cations substitution. Optical properties, crystal field strengths, and thermal stabilities of the solid solution phosphors are studied as a function of x. After complete replacement of Sc3+, the as‐fabricated FR pc‐LED emits at 750 nm with 65.7% blue‐to‐FR quantum conversion efficiency and consequently offers an electricity‐to‐FR light conversion efficiency over 30%. Moreover, the solid solution phosphors show high quenching temperatures in the range of 580–610 K. The results can advance the development of efficient FR phosphors and pc‐LEDs for various applications.

Rapid Nondestructive Detection Enabled by an Ultra‐Broadband NIR pc‐LED

“…NIR phosphors-converted light-emitting diodes (pc-LED) activated by commercial blue chips are one of the ideal light sources owing to their features of low cost, compact size, high energy efficiency, and environmental friendliness. [6][7][8][9][10] Cr 3+ ion with a 3d 3 electronic configuration is at the core of NIR phosphors due to its broad absorption spanning the deep ultraviolet (UV) and visible that coincides with the emission of commercial UV, blue, and red LED chips. Meanwhile, Cr 3+ ion as an NIR emitter exhibits great superiority over the lanthanide (Pr 3+ , Nd 3+ , Tm 3+ , Eu 2+ , etc.)…”

Glass‐Crystallized Luminescence Translucent Ceramics toward High‐Performance Broadband NIR LEDs

“…[ 12 ] Nevertheless, the fundamental problem for Cr 3+ activated phosphors is the small absorption cross‐section (10 −19 –10 −20 cm 2 ) of Cr 3+ as a result of the parity‐forbidden nature of intraconfigurational d–d transitions ( 4 A 2 → 4 T 1 / 4 T 2 ). [ 13 ] Increasing the doping concentration, [ 11 , 14 ] and introducing the odd‐parity crystal field by lattice distortion, [ 15 ] can expectedly improve the light absorption efficiency (AE), but inevitably impose serious adverse effects on IQE and thermal stability because of the enhanced (thermally activated) concentration quenching and/or the reduced structural rigidity. [ 16 ] Another knotty problem for traditional NIR pc‐LEDs with phosphor powders embedded in organic resin is the massive heat accumulation resulting from large quantum defect (>40%) in down‐converting blue light into NIR one and the very low thermal conductivity (≈0.2 W m −1 K −1 ) of organic binders, which fundamentally limit the performance of the pc‐LED devices.…”

Efficient broadband near-infrared emission induced by Nb5+ substitution for Ta5+ in GaTa1−yNbyO4:Cr3+ phosphor

“…This is similar to the conclusions reported by Xiao et al on the issue of reduced lifetime. 37 Fig. 4a and Fig.…”

“…2a). [36][37][38] The 4 A 2 (F) → 4 T 1 (P) (200-400 nm), 4 A 2 (F) → 4 T 1 (F) (400-560 nm) and 4 A 2 (F) Table 1 The metal-oxygen bond lengths (Å) and distortion indexes of GTNO:0.02Cr 3+ (y = 0, 0.1, 0.5, 0.7, 1.0) samples y = 0 y = 0.1 y = 0.5 y = 0.7 y = 1.0 In the visible light range (400-800 nm), there are two broad absorption bands peaking at 474 and 676 nm in GTNO0.02Cr 3+ (y = 0). 32,38 With increasing Nb 5+ concentration (y = 0-0.7), the broad absorption bands show a red shift in the 400-800 nm region.…”