Luminescence Temperature Quenching for Ce³⁺and Pr³⁺d-fEmission in YAG and LuAG

Abstract

The d-f emission from Ce 3+ and Pr 3+ in garnets is attracting considerable attention, especially in relation to application in white light LEDs and scintillators. An important aspect is the luminescence quenching temperature T Q . It is not trivial to determine T Q and to unravel the quenching mechanism. In this paper the T Q of d-f emission for Ce 3+ and Pr 3+ are determined by temperature dependent lifetime measurements. The results show a T Q for Pr 3+ of 340 K for Y 3 Al 5 O 12 :Pr 3+ (YAG:Pr) and 680 K for Lu 3 Al 5 O 12 :Pr 3+ (LuAG:Pr). For Ce 3+ the T Q is too high to measure. An onset of quenching above 600 K (YAG:Ce) or 700 K (LuAG:Ce) is observed. The differences in T Q between YAG and LuAG are explained by a smaller Stokes shift for the d-f emission in LuAG (∼2300 cm −1 ) compared to YAG (∼2750 cm −1 ) derived from low temperature luminescence spectra. The large difference in T Q between Ce 3+ and Pr 3+ is related to the smaller energy difference between the lowest energetic fd state of Pr 3+ and the next lower 4f 2 state ( 3 P 2 ) compared to the 5d -4f 1 ( 2 F 7/2 ) energy difference for Ce 3+ . Both observations are consistent with luminescence temperature quenching by non-radiative relaxation from the 5d state to the 4f state described by a configurational coordinate diagram and not by thermally induced photoionization.

Critical Review—Narrow-Band Emission of Nitride Phosphors for Light-Emitting Diodes: Perspectives and Opportunities

“…90 The third mode is based on the 4f-5d crossing model that is illustrated in configuration coordinate diagrams. [91][92][93] The fourth mode is the transfer of electron holes from the ground state of the activator to the valence band (VB). Bandgap.-Sufficient bandgap can ensure stability of the nitride phosphors and the presence of luminescence behavior.…”

“…Heat could be sufficient to excite electrons in the d orbitals to the CB, thereby thermally quenching the emission through non-radiative modes and adversely affecting color, efficiency, and overall device performance. 26,27 Based on a spectral pc-LED model with red and green phosphors, the target discovery and improvement toward narrow-band phosphors indicate the optimization of conversion efficiecny (CE) as predicated by bandwidths and peak positions, where CE refers to the lm/W rating. CE is calculated based on the luminous efficcay of radiation (LER) and Stokes loss.…”

CHALLENGES IN APPLICATION OF LUMINESCENT MATERIALS, A TUTORIAL OVERVIEW (Invited Review)

“…Garnets show light yields up to 60000 ph/MeV and when doped with Ce 3+ their primary decay time when excited with ionizing radiation is smaller than 100 ns, beit that in many cases longer decay components due to the presence of shallow traps and afterglow as a consequence of the presence of deep traps is observed. It is also observed that the luminescence properties and the light yield strongly depend on the material composition, see, f.e., [22][23][24][25][26][27][28][29]. Both (Y,Gd) 2 O 3 :Eu and the garnets are cubic, and transparent ceramic material can be obtained without the need for single crystal growth.…”

Editors' Choice—Thermal Quenching Analyses of Eu2+-Activated Sr-Containing Sialon Phosphors Using the Thermally Activated Cross-Over Model

“…In an attempt to investigate the relation between the compositions, structures of the host crystals, and their luminescence properties, the thermal quenching of these phosphors is analyzed. The research about the thermal quenching of phosphors have increased in these days, [19][20][21][22][23][24][25][26][27][28] and two processes of the thermal quenching are mainly considered. One is the thermally activated cross over from the excited state to the ground state; [19][20][21][22][23][24] the other is the thermal ionization from the excited state to the bottom of the conduction band (CB).…”

“…The research about the thermal quenching of phosphors have increased in these days, [19][20][21][22][23][24][25][26][27][28] and two processes of the thermal quenching are mainly considered. One is the thermally activated cross over from the excited state to the ground state; [19][20][21][22][23][24] the other is the thermal ionization from the excited state to the bottom of the conduction band (CB). [25][26][27][28] Struck and Fonger proposed a quantitative method to describe the radiative and non-radiative relaxation from excited states using a quantum mechanical single configurational coordinate (QMSCC) model.…”