Broadband NIR Phosphor Ca₂LuScAl₂Si₂O₁₂:Cr³⁺ for NIR LED Applications

Abstract

Currently, NIR analysis and detection are mainly concentrated on large-scale equipment, which is not conducive to daily use. In order to achieve the practicability and convenience of optical-electronic products, smart NIR light sources have been proposed for intelligent devices, especial the smart phone, to detect the freshness and safety of food. [7] It is essential to find a new NIR light source with high efficiency and broadband emission for these applications. Compared with the traditional NIR light source (i.e., tungsten halide lamps and laser diodes), the NIR phosphorconverted light-emitting diodes (pc-LEDs) are prepared by combining broadband NIR phosphors and blue LED chips, which have the advantages of smaller size and longer life. [8,9] Therefore, developing a broadband NIR phosphor that can be effectively excited by the blue light is the top priority for many applications.Activators excited by the blue light in NIR phosphors are mainly rare-earth and transition metal ions. Eu 2+ is a candidate, which shows broad NIR light with a peak at 740 nm and a full width at half maximum (FWHM) of 160 nm in K 3 LuSi 2 O 7 , while the intensity at 150 °C is only 59% of that at room temperature. [10] In addition to the lower thermal stability, NIR emission from rare-earth ion single-doped phosphors are often to obtain high efficiency. [11,12] On the contrary, the NIR phosphor doped with transition metal ions is easy to obtain broadband emission with good thermal stability. Cr 3+ is one of transition metal ions with 3d 3 electronic configuration, and the shell does not shield the three valence electrons. The spatial expansion of the d-electron wavefunction will be strongly interacted by the crystal field and lattice vibrations. Therefore, the Cr 3+ ions are very sensitive to the crystal field, which can be exploited to obtain NIR phosphors with high thermal stability and broadband emission by changing the crystal field environment. [13] Furthermore, the d-d transition of Cr 3+ ions usually shows a vast emission peak and absorption peak, and there is a significant absorption in the blue light. Thus, NIR phosphors doped with Cr 3+ ions have been studied widely. [14][15][16][17][18] Cr 3+ often occupies octahedrons or tetrahedrons sites in germanate NIR phosphors with wide FWHM. [19][20][21] Although the NIR phosphor based on germanate has a comprehensive emission spectrum, the low quantum Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have promising applications in food analysis, night vision imaging, and biological probes. Developing NIR phosphors with broadband emission and high efficiency has attracted immense interest. Herein, a novel NIR phosphor Ca 2 LuScAl 2 Si 2 O 12 :Cr 3+ (CLSAS:Cr 3+ ) is reported for the first time. Under the excitation of 442 nm light, CLSAS:Cr 3+ shows broadband emission from 600 to 900 nm with a full width at half maximum (FWHM) of 142 nm, benefiting from the emissions of two Cr 3+ centers in CLSAS, which is proved by the spectra and the decay curves. The internal q...

Improving and broadening luminescence in Gd2−xAlxGaSbO7:Cr3+ phosphors for NIR LED applications

“…The inten- sity decreases with increasing temperature due to the greater non-radiative transition at higher temperature. 5,39,45 Fig. 9(b) reflects the emission position as a function of temperature, which shifts slightly to the right as the temperature increases, accompanied by the gradual vanishing of the narrow peak located at 689 nm, ascribed to the decrease in crystal field strength resulting from heat-induced crystal lattice expansion.…”

Broadband Near-Infrared Luminescence in Garnet Y3Ga3MgSiO12: Cr3+ Phosphors

“…Among them, garnet is considered as an excellent host due to its typically large band gap, which can suppress the electron-phonon coupling (EPC) of Cr 3+ to the host lattice. − Cr 3+ -doped garnet NIR phosphors have been widely studied, and a series of high internal quantum efficiency (IQE) and thermal stable NIR phosphors have been reported (Table ). However, the external quantum efficiency (EQE) of the developed phosphors is usually low, which is essentially due to the low photon-absorbing efficiency of the parity-forbidden d–d transition of Cr 3+ . − Discovering broadband NIR phosphors with high EQE is of significant importance for NIR spectroscopic applications.…”

Stable Polyhedron-Cluster-Based Rigid Fluoride Framework toward Zero-Thermal-Quenching Near-Infrared Emission for Prolonged LED Applications

“…26 Usually, incorporating Cr 3+ into matrixes with a rigid crystal structure and a wide band gap (E g ) could effectively suppress the electron− phonon coupling (EPC) effect and thermal ionization processes of Cr 3+ emission. 25,26 Many Cr 3+ -doped garnet oxides, possessing a polyhedron-connected three-dimensional (3D) rigid framework as well as a large E g , exhibit good thermal stabilities. 26−28 For example, 97.4% of Cr 3+ emission at 150 °C was received in Ca 3 Sc 2 Si 3 O 12 :Cr 3+ by adding fluxes and sintering in a CO-reducing atmosphere.…”

“…Lots of high-efficiency Cr 3+ -doped NIR phosphors have been developed, such as ScBO 3 :Cr 3+ (QE = 72.8%), Ga 2– x Sc x O 3 :Cr 3+ (QE = 99%), and Gd 2.4 Lu 0.6 Ga 4 AlO 12 :Cr 3+ (QE = 92.3%). ,, However, a strong coupling of the d orbital to the phonon of the host lattice easily occurs with a result of more than 20% thermally induced emission loss at 150 °C among most Cr 3+ -based NIR phosphors . Especially, a dramatic thermal impact usually forms in high-power LED chips under high current aiming for high radiance, which prompts achieving a highly thermal stability to be the greatest challenge for Cr 3+ -doped phosphors to realize long-term practical applications . Usually, incorporating Cr 3+ into matrixes with a rigid crystal structure and a wide band gap (E g ) could effectively suppress the electron–phonon coupling (EPC) effect and thermal ionization processes of Cr 3+ emission. , Many Cr 3+ -doped garnet oxides, possessing a polyhedron-connected three-dimensional (3D) rigid framework as well as a large E g , exhibit good thermal stabilities. − For example, 97.4% of Cr 3+ emission at 150 °C was received in Ca 3 Sc 2 Si 3 O 12 :Cr 3+ by adding fluxes and sintering in a CO-reducing atmosphere .…”