The OP538FB from TT Electronics is a Phototransistor with Collector Emitter Voltage (Breakdown) 30 V, Collector-Dark Current 225 nA, Collector Emitter Voltage(Saturation) 1.1 V, Emitter Collector Voltage(Breakdown) 5 V, On-State Collector Current 2.3 to 20.5 mA. More details for OP538FB can be seen below.