Broadband near-infrared (NIR)-emitting phosphors are key for next-generation smart NIR light sources based on blue LEDs. To achieve excellent NIR phosphors, we propose a strategy of enhancing the crystallinity, modifying the micromorphology, and maintaining the valence state of Cr3+ in Ca3Sc2Si3O12 garnet (CSSG). By adding fluxes and sintering in a reducing atmosphere, the internal quantum efficiency (IQE) is greatly enhanced to 92.3%. The optimized CSSG:6%Cr3+ exhibits excellent thermal stability. At 150 °C, 97.4% of the NIR emission at room temperature can be maintained. The fabricated NIR-LED device emits a high optical power of 109.9 mW at 520 mA. The performances of both the achieved phosphor and the NIR-LED are almost the best results until now. The mechanism for the optimization is investigated. An application of the NIR-LED light source is demonstrated.

Broadband near‐infrared (NIR) phosphor‐converted (pc) LED is promising next‐generation tiny light source for smart and broadband NIR spectroscopy technology. However, NIR phosphors suffer from challenges in terms of low quantum efficiency and bandwidth. By selecting a host that has a big bandgap and weakening coupling effect among Cr3+, a novel LiGaP2O7:Cr3+ (LGAP:Cr3+) NIR phosphor that has a high external quantum efficiency (28.3%) is discovered. Under ≈450 nm excitation, LGAP:Cr3+ shows broad NIR emission from 700 to 1100 nm with a bandwidth of ≈170 nm. Importantly, the fabricated pcLED demonstrates bright broadband NIR light and an excellent performance in night vision. The results promise the use of the LGAP:Cr3+ phosphor for high‐performance broadband NIR LED that employs only one tiny blue LED chip.

Phosphor-converted (pc) white LEDs, generally installed in smartphones, are constructed by a single commercial blue LED and green/yellow/red phosphor powders. [12,13] Based on the mature pcLED technology, broadband NIR pcLED by employing phosphors that convert blue light to broadband NIR light is developed. [14,15] Commercial blue InGaN LEDs are efficient. [16] Using a single blue LED and NIR phosphors, a blue-NIR pcLED is the best solution to meet the needs of both compact dimensions and broadband NIR radiation. [17] Since the world's first broadband blue-NIR pcLED was produced by OSRAM at the end of 2016, [18] enormous progress has been achieved in broadband NIR phosphors that can be effectively stimulated by blue light. Comprehending kinds of reported NIR phosphors, Cr 3+ is believed to be one kind of the best activators due to its tuneable broadband and efficient NIR emission. [2,14,15,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Correspondingly, the radiant power of NIR light was improved from 7-18.2 mW [25,33] to 43.1-81 mW [14,21,30,31] for the NIR pcLEDs driven at 350 mA. To achieve a high NIR radiation, the key is how to simultaneously possess a high efficiency and good thermal stability in NIR phosphors. The biggest challenge is how to discover a host that can depress the electron-phonon coupling (EPC) of Cr 3+ to the host.Garnets have been regarded as excellent hosts among lots of Cr 3+ doped NIR phosphors. Because garnets usually have a large bandgap that can depress the EPC of Cr 3+ to the host lattice. In addition a high efficiency, thus, Cr 3+ manifests high thermal stability in garnets, [27][28][29][30][31] such as the silicate garnet of Ca 3 Sc 2 Si 3 O 12 :Cr 3+ (CSSG:Cr 3+ ). [30] Herein, another silicate garnet of CaLu 2 Mg 2 Si 3 O 12 (CLMSG) that has a large bandgap (5.55 eV) is noted, [34] and Ce 3+ shows excellent luminescence in CLMSG for white LEDs. [34,35] In this work, we report the CLMSG:Cr 3+ NIR phosphor for the first time. Benefiting from the large bandgap and the weakened coupling of Cr 3+ to the CLMSG host, the optimized CLMSG:5%Cr 3+ has a characteristic of good thermal stability (≈92.1%@373 K). Correspondingly, the NIR radiation reaches 34.75 mW@100 mA for the fabricated tiny NIR pcLED.