Site-Selective Spectroscopy of Garnet Crystals Doped with Chromium Ions

Abstract

Site-selective spectroscopy is a tool that can be used to uncover the presence of multiple sites available to optically active ions in host lattices. In this Article, we present techniques that can be applied to appraise the different sites that may occur in systems where charge compensation is required or in systems where such compensation is not present. We then consider some garnet crystals doped with chromium ions. For the Cr-doped garnets (YAG, GGG, GSGG, and CYMGG), we present luminescence and lifetime data over a wide temperature range, and infer not only the presence of different centers, but also the interaction among them as a function of temperature.

Boltzmann Thermometry in Cr3+‐Doped Ga2O3 Polymorphs: The Structure Matters!

“…The high-resolution spectra of the spin forbidden 2 E→ 4 A 2 transition collected at 20 K for both the polymorphs shows the splitting into two R-lines which can be now well discriminated (PLE in Figure 3a and the inset of Figure 3b). It is interesting to note the large difference between the R-line splitting energies between the two polymorphs: β-Ga 2 O 3 :Cr 3+ system is characterized by a large energy split ΔE R = 164 cm −1 , similar to the value estimated in Bi 2 Ga 4 O 9 (168 cm −1 at 80 K [20] ), while α-Ga 2 O 3 :Cr 3+ shows a small ΔE R = 34 cm −1 , similar to the values reported for the garnets GGG (36.2 cm −1 [40] ) and GSGG (31.5 cm −1 [41] ), ruby (29 cm −1 [42] ), and ZnGa 2 O 4 (38 cm −1 [43] ). The relatively higher value for the α-Ga 2 O 3 :Cr 3+ with respect to the isostructural α-Al 2 O 3 :Cr 3+ (ruby) confirms the trend when we move from gallates to aluminates as for the perovskites LaGaO 3 (24.1 cm −1 [44] ) and LaAlO 3 (5.4 cm −1 [45] ), the garnets YGG (22 cm −1 [46] ) and YAG (19 cm −1 [47] ), the mullites Bi 2 Ga 4 O 9 (168 cm −1 [20] ) and Bi 2 Al 4 O 9 (131 cm −1 [21] ), and the spinels ZnGa 2 O 4 (38 cm −1 [43] ) and ZnAl 2 O 4 (6 cm −1 [48] ).…”

Enhanced Sunlight Excited 1‐μm Emission in Cr3+–Yb3+ Codoped Transparent Glass‐Ceramics Containing Y3Al5O12 Nanocrystals

“…In addition, the relative intensity of the sharp line emission of Cr 3+ is proportional to the crystal field strength to some extent . The emission intensity of Cr 3+ : 4 T 2 → 4 A 2 transition is higher than that of Cr 3+ : 2 E→ 4 A 2 transition in the GC, which is inconsistent with the emission spectra of Cr 3+ in YAG phosphors .…”

Toward tunable and bright deep‐red persistent luminescence of Cr3+ in garnets

“…Figure (A) gives the PL spectra (λ ex =460 nm) of the Cr 3+ singly doped garnet ceramic samples at room temperature (RT), all of which show the broad band emission of Cr 3+ located from 650 nm to 1000 nm. The emission band of Cr 3+ in the LuG G sample is attributed to the typical transition of R ‐line [ 2 E ( 2 G)→ 4 A 2 ( 4 F)] peaked at 690 nm and some phonon sidebands (PSBs) due to the thermal vibration of Cr 3+ ions . When Lu 3+ in the A site and Ga 3+ in the B site are, respectively, replaced by larger cations Y 3+ /Gd 3+ and Sc 3+ , the broad band emission of Cr 3+ due to the 4 T 2 ( 4 F)→ 4 A 2 ( 4 F) transition becomes dominant and gradually shifts to longer wavelength.…”

“…Considering the high tolerability of these three cation sites (i.e., the larger dodecahedral sites are ideal for lanthanide ions [Ln 2+/3+ ], while the smaller octahedral sites are of the appropriate size for Cr 3+ ions), versatile doping strategies can be utilized to obtain different garnet matrices with different crystal fields. Considering the emission band of Cr 3+ is quite related to the crystal field strength of hosts, and can be easily tunable from the sharp R ‐line emission in the strong crystal field to the broad band emission in the weak one because of different electron‐phonon couplings, the dominant emission band of Cr 3+ in garnet is expected to be quite controllable by tailoring the local crystal fields of different hosts, which is called “crystal field engineering.”…”