Temperature dependent photoluminescence of Cr3+ doped Sr8MgLa(PO4)7

Abstract

Broad band near infrared (NIR) light sources are currently of great interest in many application areas, especially in near infrared spectroscopy (NIRS). Due to the declining availability of incandescent and halogen light sources, there is a strong demand for other efficient broad band NIR light sources. NIR phosphor converted (pc) LEDs are presently explored to realize efficient broadband NIR sources. Herein, we report on the luminescence properties of Cr3+ doped Sr8MgLa(PO4)7 (SMLP) which is a potential luminescent converter for high power broad band NIR pcLEDs. Microcrystalline powders of SMLP doped with different Cr3+ concentration were synthesized by solid state reactions and exhibit efficient near infrared broad band emission upon excitation in the blue/cyan spectral range. The emission extends from 700 to 1000 nm (FWHM = 140 nm) and is assigned to the spin-allowed 4T2→4A2 transition of Cr3+. The optical properties of Cr3+ ions in SMLP were examined in terms of spectroscopic parameters such as crystal field strength, Racah parameters, and phonon coupling parameters. The photoluminescence quenching temperature (T1/2) is a crucial parameter for blue to NIR radiation converters as the high power (In,Ga)N LEDs (pumping source) reach junction temperatures up to ∼450 K. The Sr8MgLa(PO4)7:Cr3+ phosphors reveal rather low quenching temperatures (T1/2 ≅ 300 K) mainly due to a strong electron-phonon coupling, while the presented results provide insight in factors determining thermal quenching.