Luminescence Behaviors of the New Upconversion Phosphors of Yb/Ho Co-Doped (Gd_1-<i>x</i>Lu_<i>x</i>)₃Al₅O₁₂ (x=0.1-0.5) Garnet Solid Solutions

Abstract

The metastable garnet lattice of Gd3Al5O12 (GdAG) was effectively stabilized via doping with significantly smaller Lu3+, and based on which (Gd,Lu)AG:Yb/Ho was developed in this work as a new type of upconversion phosphor. The phosphor particles calcined from the precursors synthesized via carbonate precipitation were observed to have good dispersion and fairly uniform morphologies. Optical spectroscopy found that the [(Gd1-xLux)0.948Yb0.05Ho0.002]3Al5O12 (x=0.1-0.5) garnet powders exhibit a green emission centered at ~543 nm (the 5F4,5S25I8 transition of Ho3+) and a red emission centered at ~668 nm (the 5F55I8 transition of Ho3+) under laser excitation at 978 nm. The upconversion emission intensity was found to decrease with increasing Lu3+ doping. Meanwhile, the dependence of up-conversion emission intensity on the pumping power was measured and the up-conversion mechanism was discussed in detail. The Yb/Ho codoped (Gd,Lu)AG garnet system developed herein may potentially be used as a new type of luminescent material.

Phase evolution, structure, and up‐/down‐conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho, Er, Tm)

“…Such a UC behavior is different from that of (Gd 1-x Lu x ) AG:Yb/Ho (x = 0.1-0.5) garnet, which was reported to show a stronger red than green emission. 23 The individual narrow peaks within each of the aforesaid two emission groups are known to be induced by splitting of the 5 F 4 , 5 S 2 , and 5 F 5 excited levels, as previously observed for Ho 3+ in the hosts of ScOF and Y 6 O 5 F 8 . 45,46 In general, the number (n) of excitation photons required to populate the upper emitting state under unsaturation can be obtained from the relation I em = α(P) n , 47 where I em is the intensity of UC luminescence, P is the pumping power, and α is a proportionality factor.…”

“…18 The garnet structure was also suggested to be desirable for UC luminescence, since in which the Yb 3+ sensitizer may present large ground-state Stark splitting to form a quasi-three energy level, which was expected to be able to enhance absorption of the NIR excitation energy and to improve the efficiency of energy transfer from Yb 3+ to RE 3+ for better luminescence. 19 In practice, intense green UC emission from Ca 3 (Sc 2 Si 3 )O 12 :Yb/Tb, 20 strong white emission from Lu 3 Ga 5 O 12 :Tm/Yb/Er, 21 intense NIR Stokes and blue anti-Stokes emissions from Lu 3 Ga 5 O 12 :Yb/Tm, 22 dominantly strong red emission from (Gd 1-x Lu x )AG:Yb/Ho (x = 0.1-0.5), 23 green and red luminescence from YAG:Yb/Er, 24 and absolutely strong NIR emission from Ca 3 Ga 2 Ge 3 O 12 :Cr/ Yb/Tm 25 garnets have been reported.…”

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

“…The energy transferred from Yb 3+ may effectively populate the upper level of Tm 3+ in YAG [83]. UC performances were recently studied for stabilized GAG with the compositions of [(Gd 1- x Lu x ) 0.948 Yb 0.05 Ln 0.002 ]AG ( x = 0.1–0.5, Ln = Er, Ho, and Tm) [53, 84, 85]. Despite the dilute Yb and Ln concentrations, strong UC luminescence was clearly observed in each case upon laser exciting Yb 3+ at 978 nm, as shown in figure 18 together with the mechanism of UC.…”

“…Lowered luminescence with increasing Lu incorporation and enhanced emission with increasing temperature of phosphor synthesis were found for the above UC systems. Analyzing the emission intensity against excitation power indicated that the UC luminescence may have occurred via a three-photon process for Tm 3+ and a two-photon process for both Ho 3+ and Er 3+ , which are schematically shown in the right part of figure 18 [53, 84, 85]. …”

“…Mechanisms of the UC processes are presented in the right-hand schemes. Reproduced with permission from [85], copyright 2014 by Trans Tech Publications, and [84], copyright 2014 by Elsevier.…”