A series of novel KSrY1–xErx(BO3)2 (x = 0–1) phosphors that emit near‐infrared radiation was synthesized using solid‐state methods. Pure Y and Er crystals were grown using a KF flux via the top‐seeded solution growth technique. In situ high‐temperature single crystal X‐ray diffraction, Raman spectroscopy and DFT calculations were used for characterization. Within the series, a polymorphic phase transition from space group P21/m to R3m was discovered between 550 and 600°C. The concentration dependence of the luminescence intensity was measured for the samples. A strong emission of Er3+ electron transition 4I13/2 → 4I15/2 was detected within the 1529–1549 nm range, with the maximum observed for the KSrY0.4Er0.6(BO3)2 composition. [ABSTRACT FROM AUTHOR]