Thermally Stable CaLu₂Mg₂Si₃O₁₂:Cr³⁺ Phosphors for NIR LEDs

Abstract

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.

Luminescence properties of Cr3+-doped near-infrared emissive fluoroyttrates for light-emitting diodes

“…Furthermore, the spectral FWHM slowly expands from 102 to 115 nm as the temperature increases from 298 to 423 K, which originates from the increasing electron–phonon coupling effect. 43 An important parameter of activation energy (Δ E ) is employed to depict the thermal-quenching behaviour of the RNYF:0.10Cr phosphor, which is calculated by the modified Arrhenius equation: 44 where I 0 and I T represent the PL intensities at given temperatures of 298 K and T , respectively. k is 8.629 × 10 −5 eV K −1 and A is a constant.…”

Achieving stable photoluminescence by double thiacalix[4]arene-capping: the lanthanide-oxo cluster core matters

“…In additional to moisture stability, the thermal stability of phosphors is another important aspect that is critical for practical applications (the operation temperature of an LED device can reach 150 °C). 59–62 Before analyzing the luminescent stability at high temperature, we first look at the structural stability of 2 and 4 at elevated temperatures by conducting thermogravimetry analysis (TGA). The TGA curve of 2 do not show significant weight loss until 327 °C, which likely because of the decomposition of ligands (Fig.…”

How to Obtain Anti‐Thermal‐Quenching Inorganic Luminescent Materials for Light‐Emitting Diode Applications

“…a novel NIR CaLu 2 Mg 2 Si 3 O 12 :Cr 3+ phosphor with an EQE of 20.7% and high thermal stability (92.1%@100 °C). [34] Upon blue light excitation, this NIR phosphor exhibits broad NIR emission (650-900 nm) with a FWHM of ≈120 nm. The fabricated NIR pc-LED demonstrates bright NIR light (34.75 mW@100 mA) with photoelectric efficiency of 11.6%.…”