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.
