Thermally Robust Broadband Near-Infrared Luminescence in the NaGaP₂O₇:Cr³⁺ Phosphor

Abstract

The near-infrared (NIR) phosphor-converted lightemitting diode (pc-LED) is an emerging portable light source and has multifunctional applications based on spectroscopic technology. Nevertheless, it is still difficult to develop broadband NIR materials with strong resistance toward thermal quenching. In this work, a thermally robust broadband NIR phosphor NaGa-P 2 O 7 :Cr 3+ was reported, which has an emission peak located at 793 nm, and the emission spectrum covers 650−1100 nm with a full width at half-maximum (fwhm) of 115 nm. The emission intensity at 150 °C was surprisingly maintained as 85.45% of that at 25 °C, indicating an outstanding ability to resist thermal quenching. A systematic investigation of aspects such as structural rigidity, the band gap of the host, and the electron phonon coupling effect was carried out to understand the mechanism of thermally robust luminescence in this material. Finally, the NaGa 0.94 Cr 0.06 P 2 O 7 NIR phosphor and 450 nm InGaN LED chip were combined to produce a prototype NIR light source. This device generates a NIR output power of 44.43 mW and a photoelectric conversion efficiency of 10.4% when driven at 150 mA, demonstrating a good performance of this material for practical applications.

Efficient and Tunable Near-Infrared Luminescence in Cubic Phosphate K2AlTi(PO4)3:Cr3+ for Spectroscopy Applications

“…The crystal structure and electronic band structure of K 2 AlTi(PO 4 ) 3 was first reported by Zhao et al, which has a langbeinite-type structure and a direct band gap ( E g ) of 4.62 eV . This band gap value surpasses many hosts of efficient materials, including LiInSi 2 O 6 ( E g = 3.45 eV), KGaP 2 O 7 ( E g = 4.39 eV), and Ca 3 Sc 2 Si 3 O 12 ( E g = 4.21 eV). ,, Using this structure, the structural rigidity of this material was estimated by DFT calculations, which generating a Debye temperature (Θ D ) as high as 914 K. This value is also much higher than that in most of hosts of efficient Cr 3+ -activated materials, such as GaTaO 4 (Θ D = 567 K), LiInSi 2 O 6 (Θ D = 550 K), and ScBO 3 (Θ D = 799 K). , Obviously, the ultrahigh structural rigidity and wide band gap of this compound suggest a promising luminescence performance that can be expected when doping with the Cr 3+ ion.…”

“…11,33,34 Using this structure, the structural rigidity of this material was estimated by DFT calculations, which generating a Debye temperature (Θ D ) as high as 914 K. This value is also much higher than that in most of hosts of efficient Cr 3+activated materials, such as GaTaO 4 (Θ D = 567 K), LiInSi 2 O 6 (Θ D = 550 K), and ScBO 3 (Θ D = 799 K). 27,35 Obviously, the ultrahigh structural rigidity and wide band gap of this compound suggest a promising luminescence performance that can be expected when doping with the Cr 3+ ion.…”

Broadband near-infrared luminescence in a cubic pyrophosphate Al0.5Ta0.5P2O7:Cr3+ phosphor for multi-functional applications

“…Generally, rare earth ions Eu 2+ and several transition metal ions (Cr 3+ , Ni 2+ , and Mn 2+ ) are preferred to be selected as activators for broadband NIR materials. 1,[23][24][25][26][27][28][29][30][31] Particularly, Cr 3+ when introduced into a weak octahedral crystal field exhibits broadband excitation in the blue light region and tunable NIR emission depending on crystal field strength, making it an ideal activator to convert blue light from a commercial InGaN LED into broadband NIR light. [32][33][34][35][36][37][38][39] Therefore, finding a suitable host for Cr 3+ is the main challenge for the designing of broadband NIR phosphors.…”

Infrared to Short-Wave Infrared-Emitting Phosphors for Light-Emitting Diode Applications

“…Coordination selection is crucial for studies on infrared phosphors. Various Cr 3+ -doped phosphors (e.g., oxide-based La 3 Ga 5 GeO 14 :Cr 3+ , boride-based ScBO 3 :Cr 3+ , diphosphate-based NaGaP 2 O 7 :Cr 3+ , phosphate-based Sr 9 Sc­(PO 4 ) 7 :Cr 3+ , and fluoride-based LiMGaF 6 :Cr 3+ ) have been commonly used as NIR phosphors. − Cr 3+ must be in a six-coordinated environment to exhibit photoactivity. Thus, the phosphor structure must have at least six-fold coordination, such as in AlO 6 , GaO 6 , and ScO 6 . − Similar crystal field studies may be centered on other transition metals …”