Tunable magnetic and fluorescent properties of Tb3Ga5O12 nanoparticles doped with Er3+, Yb3+, and Sc3+

Deep red upconversion photoluminescence in Er3+‐doped Yb3Ga5O12 nanocrystalline garnet

“…In the singly Er 3+ ‐doped solids excited at ≈980 nm, the green‐to‐red UCPL emission intensity ratio, originating from the respective relaxation transitions of the Er 3+ : 4 F 7/2 / 2 H 11/2 / 4 S 3/2 → 4 I 15/2 and Er 3+ : 4 F 9/2 → 4 I 15/2 , decreases with increasing Er 3+ ions concentration 51–53 . Such decrease may be explained by the change of the UCPL dynamics from the lightly Er 3+ ‐doped to the moderate/heavily Er 3+ ‐doped hosts 54,55 .…”

“…However, in many lightly Er 3+ ‐doped bulk and nanocrystalline hosts, such as Gd 3 Ga 5 O 12 , 27 Ge 25 Ga 8 As 2 S 65 , 55 ZrO 2 , 59 Lu 2 O 3 , 60 BaTiO 3 , 61 Na 0.5 Bi 0.5 TiO 3 , 62 Ba 3 Lu 4 O 9 , 63 GdOCl, 64 NaYF 4 65 or RbGd 2 Cl 7 , and RbGd 2 Br 7 , 66 the green UCPL emission dominates over the red UCPL. Compared to that, the increase of the Er 3+ ion concentration in a solid shortens the interatomic distance between the adjacent Er 3+ ions, and it results in the decrease of the green‐to‐red UCPL emission intensity ratio 49–56 . This suggests that additional UCPL pathways to the above‐mentioned GSA/ESA1 and/or GSA/ESA2 mechanism populating the Er 3+ : 4 F 9/2 level or bypassing the population at the Er 3+ : 4 F 7/2 / 2 H 11/2 / 4 S 3/2 energy levels are inevitably present.…”

“…Compared to that, the increase of the Er 3+ ion concentration in a solid shortens the interatomic distance between the adjacent Er 3+ ions, and it results in the decrease of the greento-red UCPL emission intensity ratio. [49][50][51][52][53][54][55][56] This suggests that additional UCPL pathways to the above-mentioned GSA/ESA1 and/or GSA/ESA2 mechanism populating the Er 3+ : 4 F 9/2 level or bypassing the population at the Er 3+ : 4 [51][52][53][54][55][56][67][68][69] Therefore, after the GSA/(ESA1+ETU1) process, the Er 3+ : 4 F 9/2 energy level may be populated via the population of the Er 3+ : 4 I 13/2 energy level, for example, by the CR2 process followed by ESA2 and/or ETU2 or directly via the CR1 process (see Figure 6). Both the CR1 and CR2 processes bypass the population at the Er 3+ : 4 F 7/2 / 2 H 11/2 / 4 S 3/2 energy levels responsible for the green UCPL emission.…”

“…At the low Er 3+ and high Yb 3+ doping levels of the Er 3+ /Yb 3+co-doped samples, the ETU and CR processes between Er 3+ ions may be omitted due to the longer interatomic distances between the adjacent Er 3+ ions. [51][52][53][54][55][56] However, the interatomic distance between the adjacent Er 3+ and the Yb 3+ ions in lightly Er 3+ -doped and heavily Yb 3+ -codoped hosts, such as Yb 14.99 Er 0.01 Ga 25 O 60 garnet, may be sufficiently short making the Yb 3+ ↔ Er 3+ ETU processes probable. 33,34 Moreover, the absorption cross-section of the Yb 3+ : 2 F 7/2 → 2 F 5/2 transitions are notably larger than that of the Er 3+ : 4 I 15/2 → 4 I 11/2 transitions but in resonance.…”

“…In the singly Er 3+ -doped solids excited at ≈980 nm, the green-to-red UCPL emission intensity ratio, originating from the respective relaxation transitions of the Er 3+ : 4 F 7/2 / 2 H 11/2 / 4 S 3/2 → 4 I 15/2 and Er 3+ : 4 F 9/2 → 4 I 15/2 , decreases with increasing Er 3+ ions concentration. [51][52][53] Such decrease may be explained by the change of the UCPL dynamics from the lightly Er 3+ -doped to the moderate/heavily Er 3+ -doped hosts. 54,55 At the low Er 3+ doping level, the UCPL emission is a result of the occurrence of the GSA Er 3+ : 4 I 15/2 → 4 I 11/2 followed by the excited state absorption (ESA), that is, Er 3+ : 4 I 11/2 → 4 F 7/2 (ESA1) or Er 3+ : 4 I 13/2 → 4 F 9/2 (ESA2) [54][55][56] as is presented in Figure 6.…”