Rb₄Li₂TiOGe₄O₁₂: A Titanyl Nonlinear Optical Material with the Widest Transparency Range

Abstract

Practical mid‐infrared (MIR) coherent light beams generated by frequency conversion in nonlinear optical (NLO) crystals are indispensable in time‐resolved infrared vibrational spectroscopy, remote light detection and ranging, and free‐space communications. Herein, a new titanyl germanate Rb4Li2TiOGe4O12 (RLTG) MIR NLO crystal was obtained by heavier element substitution. It features a complicated structure network composed of compressed TiO5 square pyramids and distorted GeO4 tetrahedra, separated by Rb+ and Li+ cations. More importantly, RLTG exhibits concurrently short ultraviolet (0.28 μm) and long IR (5.58 μm) transmittance cutoffs, fully covering the atmospheric transparent window of 3–5 μm. Related to the short UV cutoff, it shows a higher laser‐induced damage threshold in comparison to commercial MIR NLO crystals, about twice that of KTiOPO4 (KTP) and 50 times that of AgGaS2 (AGS).

La3Ga5M0.5Sn0.5O14, (M = Ge, Si): Design and Synthesis of Two Langasite Nonlinear Optical Materials with Large Second Harmonic Generation and Birefringence Induced by Distorted (Sn/M)O6 Octahedra

“…and d 0 transition metal cations (Ti 4+ , Nb 5+ , Ta 5+ , V 5+ , etc. ), 29−31 such as Pb 3 Ga 2 Ge 4 O 14 (5.8 × KDP), 32 Pb 3 Te(Zn 2 Ge)Ge 2 O 14 (PTZGO, 13 × KDP), 33 Li 3 (OH)PbSiO 4 (21 × KDP), 34 Ba 4 Bi 2 (Si 8−x B 4+x O 29 ) (x = 0.09) (BBSBO, 5 × KDP), 35 Cs 2 Bi 2 OSi 2 O 7 (CBSO, 3.5 × KDP), 36 Li 2 Ge(IO 3 ) 6 (20 × KDP), 37 Na 2 Ge(IO 3 ) 6 (15 × KDP), 38 × KDP), 40 Ba 2 TiOSi 2 O 7 (5.5 × KDP), 41 43 and KNbSi 2 O 7 (6.7 × KDP). 44 However, the SCALP cations and d 0 transition metal cations may cause a red shift of the absorption edge.…”

“…and d 0 transition metal cations (Ti 4+ , Nb 5+ , Ta 5+ , V 5+ , etc. ), − such as Pb 3 Ga 2 Ge 4 O 14 (5.8 × KDP), Pb 3 Te­(Zn 2 Ge)­Ge 2 O 14 (PTZGO, 13 × KDP), Li 3 (OH)­PbSiO 4 (21 × KDP), Ba 4 Bi 2 (Si 8– x B 4+ x O 29 ) ( x = 0.09) (BBSBO, 5 × KDP), Cs 2 Bi 2 OSi 2 O 7 (CBSO, 3.5 × KDP), Li 2 Ge­(IO 3 ) 6 (20 × KDP), Na 2 Ge­(IO 3 ) 6 (15 × KDP), Li 2 K 4 TiOGe 4 O 12 (2 × KDP), Rb 4 Li 2 TiOGe 4 O 12 (2 × KDP), Ba 2 TiOSi 2 O 7 (5.5 × KDP), Li 2 Rb 4 [(TiO)­Si 4 O 12 ] (4.5 × KDP), K 3 Nb 3 Ge 2 O 13 (17.5 × KDP), and KNbSi 2 O 7 (6.7 × KDP) . However, the SCALP cations and d 0 transition metal cations may cause a red shift of the absorption edge. − In a langasite structure, introducing the heavy ion Sn 4+ , the SHG response of La 3 Ga 5 SnO 14 (LGSn) can be enhanced (∼15.4 × KDP) without using the SOJT effect, which is about three times that of the La 3 Ga 5 SiO 14 (LGS) crystal .…”

Na6Sn3P4S16: Sn(ii)-chelated PS4 groups inspired an ultra-strong SHG response

“…8,9 Mid-infrared (IR) lasers have also shown significant applications in remote communication and IR detection. [10][11][12][13] Unfortunately, a few conventional commercial IR NLO crystals, such as AgGaQ 2 (Q = S, Se) 14 and ZnGeP 2 , 15 with several inherent defects such as a low laser damage threshold (LDT), harmful two-photon absorption and small birefringence, have hindered their range of application. Limited by the property requirements (wide IR transmission range, strong second harmonic generation (SHG) response, broad optical bandgap and large optical anisotropy) for an excellent IR NLO crystal, there is still a lack of outstanding NLO crystals for IR applications.…”

Na11Ta8P7O43: (Ta8O33) bi-capped triangular prisms connected by PO4 groups resulting in a phase-matched second harmonic response

“…KTiOPO 4 ), one of us proposed that the more isolated the titanium group in the crystal, the shorter the UV transmittance cutoff edge and the higher the laser-induced damage threshold (LIDT). And a new titanate Rb 4 Li 2 TiOGe 4 O 12 (RLTG) 10 has been successfully synthesized and it does show a shorter UV cutoff edge and higher laser-induced damage threshold than KTP (RLTG: 0.28 μm, 6.8 GW cm −2 vs. KTP: 0.35 μm, 3.4 GW cm −2 ). At the same time, phosphate is also a suitable system for exploring NLO crystals because of its rich structure (including the isolated group (P n O 3n+1 ) (n+2)− , ring (P n O 3n ) n− , and chain (PO 3 ) ∞ ), 11 low growth temperature and a short UV cutoff edge.…”

“…KTiOPO 4 ), one of us proposed that the more isolated the titanium group in the crystal, the shorter the UV transmittance cutoff edge and the higher the laser-induced damage threshold (LIDT). And a new titanate Rb 4 Li 2 TiOGe 4 O 12 (RLTG) 10 has been successfully synthesized and it does show a shorter UV cutoff edge and higher laser-induced damage threshold than KTP (RLTG: 0.28 μm, 6.8 GW cm −2 vs. KTP: 0.35 μm, 3.4 GW cm −2 ).…”